TRANSACTIONS OF SECTION K. 1033 



character •whatsoever, heyond their origin from a so-called sporophyte, carries its 

 own refutation.' Now, as a matter of fact, Pringsheim's description and figures of 

 (Edogonium give scanty details ; in most of the germinating zygotes the nuclei 

 themselves are not clearly shown ; much less the details of behaviour of those nuclei 

 on germination. Klebahn has described the fusion of the sexual nuclei in GMo- 

 ffonium, but I am not aware that he, or anyone else, has yet made detailed obser- 

 vations on the nuclear condition of the zoospores, or the changes which take place 

 in the germinating egg. Till this is done I submit that it is premature and unde- 

 sirable to make such assertions as those of Dr. Scott and Professor Ward. We 

 now know that important nuclear changes do take place on the germination of the- 

 zygotes of certain Algaj and Fungi. These changes are connected with a division 

 of the nuclei into four, which is the number of the zoospores usually produced 

 on germination in QLdoffonium ; the details may differ, but in the zygotes of Clos- 

 terium and Cosmarium, and in the formation of the auxospores of Mhopalodia, 

 Klebahn has demonstrated this division into four ; also Chmielewsky has described 

 a similar production of four nuclei in the germinating zygotes of Spirogyra. 

 When it is further stated that in some of these cases there is good reason to think 

 that a reduction of chromosomes is connected with the division into four, just as 

 a reduction is now known to accompany the tetrad division in Ai'chegoniate and 

 Phanerogamic plants, it is plain that such cases as that of Qildogonmm ought not 

 to be assumed to support an homologous view without any fresh observation of 

 the facts. 



With the whole question of alternation, the nuclear details and differences in 

 number of the chromosomes on division are now intimately bound up. Though 

 the observations are still few, so far as they go they are consistent with the 

 generalisation first stated by Overton, and elaborated by Strasburger as regards the 

 Archegoniate and Phanerogamic plants. It has now been seen in cases drawn 

 from various groups that the cells of the gametophyte show a certain number (w) 

 of chromosomes, while those of the sporophyte show on nuclear division double that 

 number {2)i) of chromosomes. Since Section K has had the advantage of a state- 

 ment on this subject from Professor Strasburger himself at Oxford, and as Dr. 

 Scott also discussed the matter at Liverpool, I need not enlarge. I shall only 

 remind you that Strasburger took up the position that the number of chromosomes 

 which appears in each sexual nucleus is that original number which the ancestors 

 possessed in a pre-sexual period ; while the reduction of the double number which 

 results from sexual fusion is, in his opinion, to be regarded as an atavistic process. 

 As far as investigation has yet gone, I see nothing to prevent the acceptance of 

 this as a provisional theory. 



It is now well known, however, from the observations of Farmer and of 

 Strasburger, that the nuclear conditions of Fucus are peculiar ; that the reduction 

 only takes place on the formation of the sexual oi-gans themselves, and that the 

 Fucus plant, like a sporophyte in the Archegoniate series, has the double number 

 of chromosomes. At first sight this might appear to be a fatal difficulty, arid 

 Dr. Scott, attributing to the adherents of the antithetic theory views from which 

 I personally dissent, has landed them in a seeming reductio ad abswdmn. He 

 himself does ' not think we are as yet in a position to draw any morphological con- 

 clusions from these minute differences, interesting as they are.' But we need not 

 accept either of these extreme positions, if only a certain elasticity of theory be 

 maintained, which should come naturally to adherents of polyphyletic develop- 

 ment. I think the difficulty will chiefly be felt by those who, like some of the 

 earlier writers on alternation, attempt to reduce all plants which show sexuality 

 to one stiff scheme ; this has been found to fail in the case of alternation, and a> 

 healthy recognition of various types of alternation has been the consequence. So' 

 in the matter of chromosomes, and of the position which the event of reduction 

 holds in the life-cycle ; difficulties such as this in Fucus may be anticipated, if we 

 assume that all plants will conform to one plan. But Strasburger has not con- 

 sidered it necessary to cast aside the nuclear details as a basis for morphological 

 conclusions, because all plants investigated do not fall in with a preconceived 

 scheme. On grounds of comparison of behaviour of the nuclei before and afte? 



