ZOOLOGY AND BOTANY, MICROSCOPY, KTC. 279 



pyrenoid, a densely-staining body in the centre of a radiating chromato- 

 phore, its prominence being directly proportional to its opportunities for 

 pbotosynthetic activity. The pyrenoid is actively concerned in the 

 elaboration of soluble " Floridean starch " diffused through the cyto- 

 plasm. (2) The spermatium-nucleus is in prophase of mitosis when the 

 spermatium escapes, and divides after the latter has become attached to 

 the trichogyne ; hence the; spermatium is the homologue of an 

 antheridiura. (3) Several male nuclei may pass into the trichogyne, 

 but only one enters the carpogonium. (4) A trichogyne nucleus is only 

 occasionally formed, and, when present, breaks down very quickly. 

 (5) The fusion of gamete nuclei involves a fusion of the chromatic 

 nucleoles. (C) Chromosome redaction occurs with the first division of 

 the zygote nucleus. The threads of the delicate reticulum thicken and 

 shorten, and finally take on a parallel arrangement. A fusion of threads 

 then apparently takes place, followed by condensation of material to form 

 eight bivalent chromosomes, when they become differentiated as eight 

 pairs of chromosomes distributed about the nuclear cavity in a clear 

 stage of diakinesis. The sixteen chromosomes of these eight pairs are 

 segregated by the first mitosis, which is therefore a reduction division. 



(7) The chromosome number is eight throughout all nuclear divisions in 

 the history of the plant, except the first mitosis of the zygote nucleus. 



(8) Vegetative mitoses are best studied in the cells of the developing 

 cystocarp. The resting nucleus contains a large nucleole and a reticulum 

 of delicate threads. Approaching mitosis is indicated by the appearance 

 of numerous granules (where the threads cross), which, increasing in size, 

 are brought together by the contraction of the threads, fusing succes- 

 sively until the eight chromosomes are differentiated. The spindle is 

 intranuclear, and conspicuous polar structures are present. The 

 nucleolus, empty in appearance, takes a position during metaphase on 

 the edge of the equatorial plate, outside of the spindle, and apparently 

 disappears with the breaking down of the nuclear membrane. The two 

 sets of daughter-chromosomes during telophase severally organize a 

 chromatin nucleole from which material is later distributed as a network 

 throughout the resting nucleus. (9) The nucleus left in the carpospore 

 cyst after the first division of the carpospore nucleus may again divide, 

 but the resulting nuclei do not become completely organized and soon 

 break down. (10) Since the reduction, as in Scinaia and Goleochsete, 

 takes place with the first mitosis of the zygote nucleus, the cystocarp of 

 Nemalion is not sporophytic in character, and there is no cytological 

 alternation of generations in this plant. A. G . 



Distribution of certain British Algae. — A. D. Cot'ion {Journ. Bui., 

 1914, 52, 35-40). A discussion on the distribution of certain marine 

 algfe in the British Isles, which calls for explanation on grounds of dis- 

 continuity or for some other reason. Ptilota plumosa, GalUthamnion 

 arbuscula, and Codium mucronatum var. atlanticum are specially dealt 

 with. In the absence of adequate explanation of their absence from the 

 Cornish coasts and their peculiar distribution in Wales, it is suggested 

 that a study of the effect of adverse currents in hindering the dispersal 

 of spores might solve the problem. E. S. G. 



