ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 703 



by a papilla from the former, which works its way through the cellulose 

 walls to the antherid. The differentiation of the protoplasm is associated 

 with the appearance of an organised spherical protoplasmic body in the 

 centre of the oogone, the " coenocentrum." A conspicuous stage in 

 oogenesis is that called " zonation," when the nuclei, usually in mitosis, 

 lie at or near the inner boundary of the periplasm, and the coenocentrum 

 is very prominent in the centre of the ooplasm. The oosphere is organ- 

 ised after the stage of zonation, when one of the nuclei from near the 

 periphery returns to the interior of the protoplasm, and takes a position 

 close to the coenocentrum. 



The oosphere of Albugo Candida is usually (perhaps always) uni- 

 nucleate. At the time of zonation the tip of the antheridial tube is very 

 near, if not directly applied, to the ooplasm. As it penetrates the 

 oosphere a nucleus slips down into the swollen end whose surrounding 

 wall is later dissolved, and the sperm-nucleus is then introduced into the 

 ooplasm surrounded by a quantity of dense cytoplasm. The sperm- 

 nucleus approaches the female nucleus, and slowly fuses with it in close 

 proximity to the coenocentrum. The coenocentrum is not a permanent 

 structure in the protoplasm, but becomes gradually disorganised. 



Nuclear Phenomena in the Ustilaginese.* — Prof. R. A. Harper has 

 carefully investigated the cell-fusions which occur in Ustilago antherarum, 

 Scabiosse, Maydis, and carbo, and has come to the conclusion that they 

 are not of a sexual nature. In cultures 2 or 3 days old, when the 

 supply of nutriment is deficient, two conids lying side by side put out 

 protuberances which fuse at the apex, the protoplasm of the two cells 

 coalescing. This is not followed by any fusion of the nuclei or nuclear 

 substance. It is always accompanied by an increase in volume of the 

 cells and of the amount of protoplasm contained in them. A similar 

 fusion may also take place between the two basal cells of a 3 -celled 

 promycele. The apical cell then, as a rule, degenerates, or fuses with 

 an adjacent single sporid. The multiplication of fused sporids is effected 

 by direct budding, or by a 2-3-celled germ-tube. The author compares 

 this process with similar ones in other Fungi and in Algae, where there 

 is a distinct non-sexual fusion of the protoplasm of different cells. Its 

 purposes appear to be an increase of the vegetative substance, a more 

 equable distribution of nutrient materials, and a greater power of resist- 

 ance to unfavourable vital conditions. 



Haustoria of the Erysipheae.f — Mr. Grant Smith has followed out 

 the development of the haustoria in several species of Erysipheae, 

 especially in Erysiphe communis, parasitic on Geranium maculatum. The 

 absorbing organ consists of a slender proximal portion, the neck, pene- 

 trating the epidermal wall of the cell, within which it enlarges into a 

 vesicular distal portion with a thin wall. The vesicle is filled with a 

 delicate spongy protoplasm. The mature haustorium always contains 

 one nucleus. It is almost always surrounded by a thick sheath-like 

 layer, which does not belong to the protoplasm of the host-cell, as de 

 Bary supposed, but consists of disintegrated cellulose from the cellulose 

 ingrowth through which the haustorium has made its way. Slight 



* Trans. Wisconsin Acad. Sci., xii. pp. 475-98. See Bot. Centralbl., lxxxiii. 

 1900) p. 112. f Bot. Gazette, xxix. (1900) pp. 153-84 (2 pis.). 



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