Sperm-cells in A sclepias Cornuti , Decctisne. 143 
the literature, speculating on the probable development of the 
pollen-grain directly from the mother-cell. Then follow the 
results of his own researches. He considers the phenomenon 
of numerical reduction as the criterion for the pollen-mother- 
cell, and on this basis he considers the long cells which give 
rise to the individual cells of the pollinium as the mother-cells 
of the pollen. The full complement of chromosomes in 
A sclepias is held to be twenty, but the author states that he 
was unable to count them exactly. 4 About ten ’ chromosomes 
were counted on the equatorial plate of the first division of the 
pollen-mother-cell. 
The daughter-nuclei resulting from the first division of the 
pollen-mother-cell come to the full resting condition. The 
second division the author considers as 4 homotypical/ but 
states that this cannot be proved on account of the smallness 
of the elements on the nuclear plate. Rod-shaped bodies are 
not figured, but the contents of many of the pollen-grains 
are described as especially coarse-grained, and eagerly de- 
vouring the stain. Possibly the rod-shaped bodies are here 
referred to. 
The fact that the young pollen-grain divides into a larger 
vegetative and a smaller generative cell is mentioned and the 
completed division shown, but the karyokinesis is not figured. 
Centrosomes were not found, and the author inclines very 
strongly to the opinion that they do not exist at all in the 
higher plants. 
The above three papers all leave the identity of the pollen- 
grain and its ontogeny in Asclepias an open question, since the 
peculiarities of the division are so different from those observed 
heretofore in other types, and have led many to believe that 
a shortening of the process takes place in the members of this 
genus. It would remain an open question until it was proved 
that all the divisions concerned, up to and including the forma- 
tion of the sperm-cells, are exactly the same in all essential 
points in Asclepias as those which occur in other Angiosperms. 
This identity is established for the first time by the develop- 
mental history as traced in the foregoing paper. 
