174 BOTANICAL GAZETTE [SEPTEMBER 
the differentiation of sex actually is in plants in the gametophytic 
stage. 
Unless the gametes contain both sexes, parthenogenesis in homo- 
thallic forms should give rise to unisexual individuals—the male 
gamete to male and the female gamete to female individuals. So 
far as the writer is aware, no investigations have been undertaken 
with a view to confirm this assumption experimentally. Attempts 
made by the writer to determine the sexual character in the gametes 
of homothallic mucors by means of their germination before or after 
their transformation to azygospores have not as yet been successful. 
In the higher plants, parthenogenesis in the sense of the develop- 
ment of an individual from a sperm or egg cell with the reduced 
number of chromosomes is, so far as the writer is aware, not definitely 
known to occur. The sex in the apogamous seeds of Taraxacum 
for example, however, must contain male characters if the plants 
produced from them develop stamens, as seems regularly to be the 
case. 
What the essential difference between sex actually is, is as yet 
beyond conjecture, and the significance of sex in organic develop- 
ment is at present a subject of conflicting discussion. It is to be 
hoped that a further study, especially of lower forms, where the 
gametes are more closely connected with the vegetative portions 
and the zygotes formed by their union more accessible to manipu- 
lation, may lead to a better understanding of some of the funda- 
mental problems of sexuality. The present brief article is no place 
for any detailed discussion of sexuality in the various groups of 
plants. For a short general presentation of the subject, the 
reader may refer to the recent work of KisTER (13) and to the litera- 
ture therein cited. It seems not out of place, however, to S4Y . 
few words in regard to the thallic differentiation in the lower crypto 
gams, where the subject has received little attention. : 
Unisexual and bisexual forms occur throughout the plant king- 
dom, and are often to be found in the same genera. This sex 
differentiation seems to have no relation to the stage of phylogenetic 
development.. Thus while in higher animals the unisexual con® 
tion predominates, in higher plants the monoecious, ?. ¢- homophyt; 
condition is the more common. Again, the majority of the ferns 
