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1909] : CURRENT LITERATURE 63 
The determination of sex 
STRASBURGER’S latest-work deals with the time of the determination of sex, 
apogamy, parthenogenesis, and the reduction division.4 
e discussion in regard to the determination of sex is based largely upon the 
behavior of the spores of the dioecious liverwort Sphaerocarpus. Two spores of a 
tetrad give rise to male plants and the other two give rise to females. The con- 
clusion is that the sex tendencies are separated during the two mitoses by which 
the four spores are formed from a mother cell. In the homosporous pteridophytes 
with monoecious prothallia, the expression of the sex tendency, as shown by the 
formation of antheridia and archegonia, does not take place so early, and in 
heterosporous pteridophytes all the spores of a tetrad, and even of a sporangium, 
produce plants of one sex. This is true also of spermatophytes, all of which have 
strictly dioecious gametophytes. STRASBURGER concludes, as had also CORRENS 
and Nott, that the egg tends to produce females, and he believes that the mitoses 
in the pollen mother cell separate male tendencies of unequal vigor, so that, in 
dioecious plants, two microspores of a tetrad will give rise to sperms, which, in 
fertilizing the egg, are prepotent over the female tendency and so will produce 
males. The other two microspores of the tetrad will give rise to sperms which are 
not able to overcome the female tendency of the egg, and hence it will produce 
females. The hybrid obtained by pollinating Fragaria virginica with the pollen 
of F. elatior has been explained as a case of merogeny, but STRASBURGER found that 
fertilization occurs regularly, and that both male and female plants are produced. 
All the plants, however, resemble the male. This shows that the heritable char- 
acters of one of the nuclei which unite in fertilization can dominate the other. 
There is, as yet, no cytological evidence of the separation of sex-determining struc- 
tures in plants. 
Aside from a critical review of the literature, the discussion of apogamy is 
based principally upon an investigation of Wikstroemia indica, and 62 of the 88 
figures illustrate critical stages in the life-history of this plant. As in other apoga- 
mous forms, the chromosome number is higher than in normal related species. In 
the pollen mother cells the mitoses differ from those of normal plants, and pollen 
tubes are never formed. The first mitosis in the megaspore mother cell shows 
some abnormalities. A wall is formed between the two daughter nuclei, but at 
the next mitosis, which usually occurs only in the lower cell, no wall is formed. 
An eight-nucleate embryo sac with a 2x egg is formed from the lower cell, and 
from this egg the 2x embryo is formed without fertilization. STRASBURGER 
regards this as a case of apogamy (Eiapogamie), and would reserve the term 
parthenogenesis for the development of an embryo from an egg with the reduced 
number of chromosomes. ‘The reason for the discrimination is that he regards 
the 2x eggs as practically already fertilized. 
+ STRASBURGER, Epuarp, Zeitpunkt der Bestimmung des Geschlechts, Apogamie, 
Parthenogenesis und Reduktionsteilung. Histologische Beitrage VIL. 8vo. ppv) 
- 124. pls. I-3. Jena: Gustav Fischer. 1909. M. 6,50. 
