ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
637 
£. Physiology. 
(1) Reproduction and Embryology. 
Morphology and Physiology of the Sexual Process.* — M. W. 
Chmielewskij has investigated this subject in some of the lower plants, 
especially Algae. He finds that, in Spirogyra, when the cells put out 
their conjugating processes, the tannin, which has up to that time been 
abundant in the cell-sap, disappears, while the albumen dissolved in 
the cell-sap passes into another modification. The proportion of these 
substances in the cell-sap varies with the conditions of vegetation, being 
largest during the period of rest, and being gradually used up during 
active growth. When the cells assume their sexual character, large 
quantities of starch and oil-drops are stored up in the chlorophyll-bands. 
When a young zygote of Spirogyra is made transparent without 
destroying the chlorophyll, two chlorophyll bands are readily recognized 
in it ; the one derived from the female cell is coiled spirally, that from 
the male cell irregularly. This latter undergoes changes as the zygote 
developes ; the pyrenoids and starch-grains disappear, the colour of the 
band changes from green to yellow-brown, and the band breaks up into 
pieces which pass into the cell-sap, where they are visible till germina- 
tion. In the meantime the female chlorophyll-band lengthens, and 
encloses the whole zygote in its coils. 
The conjugation of the male and female nuclei is (in Spirogyra 
crassa ) a much more complicated process than has hitherto been sup- 
posed. The resulting nucleus of the zygote divides, by karyokinetic 
division, into four nuclei, of which two break up into fragments and 
disappear, while the other two, the secondary nuclei, again unite into 
the definite nucleus of the zygote, which remains till germination. 
In Basidiobolus ranarum (Entomophthoracese) the nuclei of the 
sexual cells enter the beak and there divide; a daughter-nucleus from 
each remains in the beak, which separates itself from the true sexual 
cell by a septum ; the protoplasm of one of the sexual cells then 
passes into the other ; and the two nuclei coalesce after a time in the 
zygote so formed. 
The germination of zygotes (of Spirogyra) may be promoted by 
abundant access of air. The period of rest (in Spirogyra and (Edo - 
gonium) varies, according to the species, between one and six months. 
Impregnation of several Embryos.f — M. G. Chauveaud attributes 
the occasional occurrence of polyembryony to the existence of more than 
one male nucleus in the pollen-grain, rather than to the entrance of 
several pollen-tubes into the embryo-sac. Polyembryony has been 
observed in several Leguminosse, in Iris sibirica , Lilium Martagon , and 
Vincetoxicum ; in F. medium as many as five embryos have been 
observed. In those species in which polyembryony occurs, as e. g. in 
Vincetoxicum officinale, it is not uncommon for the pollen-grain to have 
three nuclei, one vegetative and two generative ; these latter have 
probably increased in number by division after the entrance of the tube 
into the micropyle. On the other hand the micropylar canal is so narrow 
* ‘Material, z. Morph, u. Phys. d. Sexualprocesses b. d. niederen Pflanzen,’ 
Charkow, 1890, 80 pp. and 3 pis. See Bot. Ceutralbh, 1. (1892) p. 264. 
t Comptes Rendus, cxiv. (1892) pp. 504-6. 
