VOLUME LIII NUMBER 4 
TIE 
BOTANICAL GAZETTE 
APRIL. i912 
OBSERVATIONS ON HETEROSTYLOUS PLANTS 
NEIL E, STEVENS 
(WITH PLATES XXI-XXIII) 
soe discovery of the ‘“‘sex determinant” or “accessory chromo- 
some”’ in the sperms of certain insects is probably the most notable 
cytological advance of the present decade. Furnishing, as it 
apparently does, a cytological basis for the predestination of sex 
at the time of fertilization, it has an important bearing on the whole 
question of the determination and heredity of sex. The condition 
found in these insects has been too widely discussed to need descrip- 
tion here. It may be briefly summed up, however, as follows: 
examination has shown that the sperms are of two classes, equal 
in number, which differ in respect to one or more of the chromo- 
somes which enter into the formation of their nuclei; and the facts 
clearly demonstrate that fertilization of the eggs by one class 
produces males, by the other class females. This difference, the 
significance of which was first suggested by McCLUunc in 1902, has 
been shown to occur in nearly a hundred species of insects (WILSON 
49, p. 57). 
Its prevalence here has suggested the possibility of a similar 
condition in all animals having separate sexes. Attempts have 
also been made to demonstrate such a condition in dioecious plants, 
but as yet no positive results have been obtained. Miss SYKES 
published in 1909 (39) a brief note on the nuclei of some dioecious 
plants. She studied Hydrocharis Morsus-ranae, Bryonia dioica, 
Lychnis dioica, Mercurialis perennis, and Sagittaria montevidensis, 
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