ZOOLOGY AND BOTANY, MICKOSCOPY, ETC. 2S3 



of Ceraniiaceag, Rhodomelefe, Delesseriacere, Grateloupiaceae, jSTemasto- 

 niaceae, Rhizophyllideae, Ghrysymenia, Ghylocladia, Gelidium, and Ploca- 

 mium. Finally, he makes a general comparison of the various types and 

 gives his conclusions. He finds unmistakable similarity between the species 

 of the Cerauiio-Rhodorneleae-Delesseriaceae group, as regards the develop- 

 ment of the vegetative organs, amounting even to a progressive series. 

 And the same may be said of the attachment-disk type. The more 

 primitive forms develop their disk irregularly, the higher forms develop 

 it by regular division of the spore. Again, in certain forms the upright 

 shoot is composed of an uncertain number of filaments, and in others 

 the number is determined. The most regular development is that in 

 which the erect organs arise from divisions of an apical cell. These 

 early variations are to be recognized in the later stages of the plant. In 

 spite, however, of the facility of grouping certain types together in a 

 phylogenetic connexion and of drawing conclusions from the study 

 of early development, the dangers of error are great. It is difficult to 

 determine which character is of primary, which of secondary importance — 

 the result of adaptability. This is shown in the attachment disk, which 

 shows great similarity in the most different germlings, while species 

 of the same genus occur, some with, some without it. It may, indeed, 

 be that the various types are in no way connected phylogenetically. For 

 instance, the development of Ghrysymenia closely resembles that of HaJy- 

 menia, whereas the formation of the fruit in the two species, which we 

 regard as a relatively stable character, is totally different. These points 

 show the danger of applying the law of biogenesis. The author suggests 

 that a comparison of the development of the Floridere must be carried 

 out on wide lines for a solution of phylogenetic problems ; wide enough 

 to determine the comparative value of characters. At present the prin- 

 cipal characters considered in classification are that of Nageli, who 

 regarded the growth of the thallus as the most important point. The 

 comparative development of the young and of the older vegetative organs 

 should be included in the general survey. 



Alternation of Generations in AlgaB.* — J. Bonnet writes a long 

 treatise on the sexual reproduction and the alternation of generations 

 in algae. He reviews the history of the subject from Hofmeister 

 and Sachs onwards, discussing fully the views of the various authors, 

 and pointing out how much the algas have been neglected in cy to- 

 logical work, compared with other plant groups. He then passes 

 in review the various groups of alga?, showing what is known of 

 each at the present time. He divides them for discussion into : 

 (1) those algae in which the zygote is itself the gonotokont. and the 

 2x generation is thus reduced to one cell ; (2) those in which the 

 zygote is not the gonotokont, and the 2 x generation is consequently re- 

 presented by more than one cell. Finally, he points out that a study of 

 the alternation of the haploid and diploid phases shows us how incon- 

 gruous a group is that of the algae. From the case in which the 2 x phase 

 is reduced to the point of being imperceptible, to the opposite extreme 

 in which it is much more extended than the x generation, there are many 



* Progressus Rei Botanicse. Jena : Fischer (1914) v., pp. 1-128 (figs, in text> 



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