Male Gametes in Pines and Allied Conifers. 171

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1 Male Gametes in Pines and Allied Conifers. 171 these rivers. At Lamberhurst it occupys the lower facings of the sandstone bridge which spans the River Teise and just before reaching Battle it is found occupying the sandstone escarpments by the roadside. At Ecclesbourne and Fairligbt Glens, Hastings, it is found fruiting regularly in April. The plants however growing on the banks of the rivers do not fruit periodically except in those situations where they are not liable to prolonged submersion during periods of flood, such as upon arches bridging streams. From the fact that Fegatella conica and Pellia epiphylla are found so extensively lining water courses and rarely elsewhere we may reasonably conclude that they owe their present distribution entirely to water carriage, not only of spores, but also of detached plants during periods of flood. We may also conclude that since these plants are able to complete their life cycle annually under the present conditions of our climate they have a greater chance of survival with us than Dumortiera and Lunularia, which show a waning sexual activity. ON THE MEANING OF THE VARIOUS FORMS OF THE MALE GAMETES IN THE PINES AND ALLIED CONIFERS. BY E. M. CUTTING, M.A., F.L.S., Demonstrator in Botany at Birkbeck College, London. IN 1892 Strasburger (17) described two unequal male cells as the product of division of the body cell in Pinus sylvestns. Each of these cells was surrounded by a very small amount of cytoplasm. As one would expect from the above description, and as Strasburger clearly shows in his figures 43 and 44, not only the cells but also the nuclei are of slightly different size. In 1894 Di.xon (7) in describing the male nuclei of Pinus sylvestris speaks of them as being of about tbe same size, evidently meaning to suggest by this that, as far as he could see, they were not quite equal, but very nearly so. In his figures showing this dissimilarity the nuclei are situated in the upper part of the pollen tuhe, that is to say the inequality is present at quite an early stage.

2 172 E. M. Cutting. Professor V. H. Blackman in his paper of 1898 (1) makes no reference to the relative size of the nuclei, but he has informed me that in one of his sections he remembers seeing two quite similar male nuclei and that they were situated very low down in the nucellar tissue just above the archegonia. Coulter in 1897 (5) reported the existence in Pinus Laricio of two similar male cells containing two equal sized nuclei*, and Chamberlain (2) in 1899 confirmed this. In 1901 Miss Ferguson (8) made a comprehensive study of the male apparatus in Pinus Strobns, P. atistriaca (which is merely a variety of V. Laricio), P. montana var. uncinata and P. rigida. Working with these she was unable to agree completely with any of the previous workers. In every case two unequal male nuclei were formed, but these remained embedded in one naked mass of protoplasm, no wall being formed between them. In some serial sections of Pinus sylvestris ovules, prepared for demonstration purposes, I have observed several pollen tubes containing male nuclei, and in all these cases there was only one cell, and enclosed in this two unequal nuclei. The smaller nucleus tyas directed towards the micropylar end of the nucellus, and in some cases lay quite close to the boundary of the protoplasm of the cell. The difference in size of the nuclei was more marked in those pairs which were near the archegonia than in those which were near the top of the nucellus. I am inclined to interpret this observation, as Miss Ferguson did in the case of Pi/ms Strobus (8), that is to say that in their journey down the nucellus the difference between the nuclei gets more and more pronounced. The instance noticed above, when Professor Blackman found equal male nuclei quite near an archegonium, seems to be against this view, and suggests that Pinus sylvestris presents a state of affairs intermediate between Pintis Strobus (8) and Piuus Laricio, as described by Coulter (5), forming at one time equal and at another time different grades of dissimilar nuclei. That is to say, if one regards the form with the equal nuclei as more primitive than the one with the unequal, Pinus sylvestris is a transition form from one state to the other. There seems to be no a priori reason against one species of a genus having equal male nuclei while another species has unequal. Indeed, such a case has been recorded in the genus Cephalotaxus, ' Coulter's figure showing the pollen tube in this condition is reproduced m Strasburger's Text Book of Botany, 3rd English Uliti 1908.

3 Male Gametes in Pines and Allied Conifers. 173 in which one species, C. drnpacea^, has equal male nuclei, and another species, C. Fortunei, unequal. Although Coulter has described equal male cells in Pinus Laricio, Miss Ferguson has recorded the existence of unequal male nuclei in Pinus austriaca, which I find is now regarded merely as a variety of P. Laricio. It is scarcely likely that a variety of any one species would agree in this respect more closely with other species tban it does with the species of which it is a variety. Moreover Strasburger in his *' Die Befruchtungsvorgange bei den Gymnospermen," says that many pines behave as does Pinus sylvestris and amongst them he mentions P. Laricio. It will be remembered that Strasburger figures unequal nuclei in the former species, and, therefore, it seems more than likely that he intended it to be understood that P. Laricio had unequal male nuclei also. Coulter and Chamberlain also say that two male cells are formed in Pinus Laricio, but Miss Ferguson says of P. Laricio, as well as of the others she has examined, that although two male nuclei are formed, they remain in the same cell. Two species of one genus, Torreya, have been described, one with two male cells (Coulter and Land on Torreya taxifglia 6 and one with two unequal male nuclei in a single cell (Miss Robertson's T. californica, 15). But one would certainly not expect so great a difference as this in a variety, especially as other species agree with the variety. I do not, therefore, think that these observations of Coulter and Chamberlain are confirmed by more modern researches. Pinus sylvestris I therefore regard as falling into line with the other pines as they have been described by Miss Ferguson (8). Professor Blackman's isolated instance of equal male nuclei in P. sylvestris is probably a reversion to the time when equal nuclei were formed. There can be little doubt that the body cell divided primitively into two equal male cells, and that the inequality of the male cells of such Conifers as Cephalotaxus Fortunei and Torreya taxifolia, and the inequality of the nuclei with the loss of the power of forming the two cells, as seen in the pines, Picea (Miyake 14), Abies (Miyake 13), &c., are recently acquired characters. Strasburger in 1892 suggested that these inequalities of the sizes of the cells (he was not aware of the cases in which no division of the cytoplasm was made between the two male nuclei) were due to the fact that in those cases only one male nucleus from one pollen grain has a Lawson (11) records equal male nuclei in C, dtufacea, but his figure 27 shows unequal nuclei.

4 »74 E. M. Cutting. chance of fertilizing an archegonium; and since his paper many other investigators have remarked that in those cases in which both the nuclei in the pollen tube have an opportunity of fusing with an egg-nucleus, two equal male cells were differentiated, while in the cases in which only one nucleus could fertilize an archegonium either unequal cells or unequal nuclei were formed (11). (4), &c. This reduction of the male cells seems to me to be connected with the differentiation of a smaller number of archegonia. When the latter are numerous, as in Jnniperus or Sequoia, they are more likely to be situated near each other, and this would necessarily offer greater chances of both male nuclei fertilizing an archegonium, while, when the archegonia are few they are scattered and offer less or no opportunity. One pollen tube comes thus to be restricted to one archegonium, and, as a response to this, the male cells and nuclei are differentiated as to size, the larger being the effective one in fertilization. As a further reduction we get the stage in which the division of the male cell is omitted, although two male nuclei are still formed'. From this point of view it follows that the reduction in the male apparatus follows the reduction in the female, and is not coincident with it. A conifer with a few archegonia might therefore still possess equal male cells if the habit of forming few and scattered archegonia had only recently been acquired in that form. Several conifers exhibit a great variety in the number of archegonia formed. Taxus baccata is a very good instance of this. It usually forms about five to eight archegonia, but Jager has reported as many as eleven, and Miss Robertson has even recorded seventeen. The latter writer also says that two archegonia sometimes occur without any intervening prothallial cells. Taxus therefore connects the Pintis- with the Sequoia- and jfuniperus-type, both in the numerical variations of the archegonia and the occasional non-development of prothallial tissue between adjacent archegonia. An unpublished observation of Professor Blackman's on Pinus sylvestris seems to me to have some bearing on the question of a wider distribution of archegonia on the prothallus. A few > This latter state mi^^ht sometimes be reached by passing through a stage in which equal male nuclei were formed, but only one cell (conipare Cephnlotaxtis drnpatca). One would however expect any reduction first to find expression in the nuclei, for the nuelear division precedes the cell division.

5 Male Gametes in Pines and Allied Conifers. 175 cases were observed in which the pollen-tube, instead of growing straight through the nucellus to the archegonia, made its way along the side of the prothallus, and having gone some distance in this direction then turned in towards the prothallus. This is strikingly like the state of affairs which Lawson has described for Sequoia (12), and without intending to suggest that this points to any very close relationship between Sequoia and Pinus, I yet think that it strengthens the view that the ancestors of the Pines at one time possessed a wider distribution of archegonia than they do at present. It may be noticed that the division and subsequent developmental history of the products of the division of the central cell of the archegonium suggests a series parallel with that of the division and history of the products of the body cell of the pollen-grain. If the above theory of the cause of the inequalities and variations of the male apparatus of the conifers be accepted, it will be seen that these variations are connected with changes in the female apparatus. Goebel (9) has already suggested that the differences to be observed in the germination of Cycadean and Coniferous pollen-grains are connected with the structure of the ovule. It would therefore seem that the male gametophyte is comparatively plastic and liable to vary with changes in its environment, and a certain amount of caution is required in using data gained from it in discussing the phylogeny of any particular group. REFERENCES. 1, Blackman, V. H. " On the Cytologica! Features of Fertilization and related Phenomena in I'inus sylvestris L." Phil. Trans. Roy. Soc, Chamberlain, C. J, " Oogenesis in Pinus Laricio." Bot. Gaz Coker, W. C. "Fertilization and Embryogeny in Ceplialofa.xtis Fortiinei." Bot. Gaz. XLIII ,, "The Gametophytes and Embryo of rodocarpiis." 13ot. Gaz. XXXIII Coulter J, M. "Notes on the Fertilization and Embryogeny of Conifers." Bot. Gaz. 23, Coulter J. M. and Land, W. J. G. " The Gametophytes and Embryo of Toircva Inxifolia." Bot. Gaz Dixon, H. N. " Fertilisation of PtH«j j)'/r<;s//ti." Ann. Bot

6 176 Review: 8. Ferguson, M. C, " The Development of the Pollen-tube and the Division of the Generative Nucleus in Certain Species of Pines." Ann. Bot. XV Goebel, K. " Organography of Plants." Jager, L. " Beitr&ge zur Kenntniss der Endospermbildung und zur Embryologie von Taxiis baccala." Flora Lawson, A. A. "The Gametophytes, Fertilization and Embryo of Cephalotaxus drupacea. Ann. Bot ,,,, " The Gametophytes, Archegonia, Fertilization, and and Embryo of Sequoia sempervirens." Ann. Bot. XVIII Miyake, K. " Contribution to the Fertilization and Embryogeny of Abies batsama." Beihefte zum Bot. Cent. XIV ,, "On the Development of the Sexual Organs and Fertilization of Picea excelsa." Ann. Bot. XVII Robertson, A. " Studies in the Morphology of Torreya californica, II." New Phytologist, Vol. III ,,,, " The Taxoidese : A Phylogenetic Study." New Phytologist, VI., 3 and 4, Strasburger, E. " Uber das Verhalten des Pollens und die Befruchtungsvorgange bei den Gymnospermen." Hist. Beit REVIEW. PLANT PHYSIOLOGY AND ECOLOGY, BY FREDERIC EDWARD CLEMENTS, PH.D., President of Botany in the University of Minnesota. 315 pages, 125 Illustrations. London, PROFESSOR CLEMENTS is one of the clearest and most logical exponents of ecology, and any contribution to the subject by him is worthy of earnest consideration. A great d^al of the substance of the work now under review has already appeared in his "The Development of Vegetation" (1904) and also in his " Research Methods in Ecology" (1905). The latter work was reviewed in these columns at some length by Dr. F. F. Blackman and Mr. A. G. Tansley.' The present text has been largely based on the two earlier works, though most of the matter is new or re-written, and, to a fairly large extent, re-arranged. The plant is first considered as an individual, with respect to factor, function, and form, and then as a member of a plant group. " The book is intended for use with classes in second-year botany in College and > NEW PHYTOLOOIST, Vol IV

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