540 Algae. 



diagnosis and a figure of each genus is supplied and a postcript on 

 the Constitution of plankton is appended. Ethel S. Gepp. 



Baker, S. M., On the causes of Zoning of Brown Sea- 

 weeds. IL (New Phytologist. IX. p. 54—67. 1910.) 



The author, continuing her research, describes her experiments 

 carried out with a view to determining the influence of periodic 

 desiccation on the germination, and also on the dehiscence-mecha- 

 nism of four species: Fucus spiralis, Ascophyllum nodosum, F. vesi- 

 culosus, F. serratus. They grow in the order mentioned from high- 

 water mark downwards. Those of the upper zones were found to be 

 capable of resisting desiccation during both germination and vege- 

 tative growth. Their receptacles are protected by being filled with 

 mucilage; and this seems to make their dehiscence-mechanism most 

 efficient when they are dry for a considerable lenght of time. Also 

 in both F. spiralis and A. nodosum the paraphyses project conside- 

 rably from the ostioles of the conceptacles; and this may be an 

 adaptation to ensure the gametes being very rapidly expelled during 

 the short time that they are covered by water. Experiments with 

 F. spiralis point to this conclusion. 



The algae growing in the lower zones have become adopted to 

 very rapid growth; they are thus able to supersede the more slow- 

 growing and protected forms, in their own zones, but at the same 

 time they have not the power of resisting desiccation, so that they 

 cannot grow in the upper zones. Also their dehiscence-mechanism 

 has become efficient for very short times of exposure; and they are 

 able to choke out any stray member of an Upper zone which attempts 

 to establish itself lower down, but which cannot compete with them 

 in the number of reproductive bodies given off. Ethel S. Gepp. 



Drew, G. H., The Reproduction and early Development 

 of Laminaria digitata and L. saccharina. (Ann. Bot. XXIV. p. 

 177—190. 2 pl. 1910.) 



The author summarizes the more important characters of the 

 plants, and describes his methods of collecting specimens, of pre- 

 serving the live specimens, of examining the reproductive areas, 

 and of cultivating the plants. He gives a detailed account of the 

 reproductive process and the development of the young plant, and 

 a summary of his results, which are as follows: 1) The Laminaria 

 plant is the gametophyte. 2) The reproduction areas consist of ga- 

 metangia and paraphyses. 3) Flagellated gametes escape from the 

 gametangia, and isogamous conjugation occurs. 4) The resulting 

 zygospore divides and gives rise to a chain or mass of cells. These 

 ma)^ be of the "2 x" type, or the reduction may occur in the 

 early divisions of the zygospore. 5) The cells of this structure 

 rupture, and their Contents grow out and form the gametophyte. 

 6) The young gametophyte consists of a flat lamina, one cell 

 thick, and is attached at its base to surrounding objects by a 

 number of unicellular rhizoids. 7) The cells of the lamina divide, 

 and eventually form the limiting and cortical layers and part of the 

 medullary tissue. 8) The stipe is formed by a modification of the 

 base of the lamina. 9) Part of the medullary tissue is formed by 

 an upgrowth of cells from te base of the rudimentary stipes. 10) A 



