REPRODUCTION 381 



tended to decrease the relative number of female blossoms on 

 cucumber plants; and Schaffner also found that in corn the sexu- 

 ality of the tassels changes with the amount of light. 



In dioecious plants such as the willow (Salix), hemp (Cannabis), 

 and mulberry (Morus), the flowers are sometimes perfect, suggest- 

 ing that both sex factors are present but only one is normally 

 expressed; and Salix has been observed (Giessler, 1927) to change 

 from staminate to pistillate. In Myrica gale, which is normally 

 dioecious, all sorts of transitions are seen. Sometimes the same 

 shoot will bear both male and female flowers, and sometimes a 

 shoot will bear male flowers one year and female the next. When 

 on the same shoot, those above tend to be female, indicating the 

 presence of a nutritional factor. One of a pair of united male twins 

 of Arisxma triphyllum was changed into a female by controlling 

 the nutrition (Schaffner, 1926). Similarly Maekawa (1925) found 

 that the corm of the Japanese Arisaema changes its sexuality from 

 male to female as it grows older. However, after it has become a 

 female, the sexuality can be reversed by growing in poor soil or 

 by removing portions of the corm or leaves. One of the best ex- 

 amples of the relative nature of sexuality is seen in Ectocarpus, an 

 alga. In this plant, the gametes may be grouped as male and fe- 

 male and these in turn can be graded, largely on the basis of size 

 and activity, into gametes of varying intensity. Thus if gametes 

 of the same sex but of very different " intensities " are brought to- 

 gether, the weaker one behaves as though of the opposite sex 

 (Hartmann, 1931). Schaffner also reports that in some species of 

 Spirogyra a filament may act as a male towards one filament and 

 as a female towards another. The conclusion, therefore, is that 

 sex is a quantitative and not a qualitative matter. The tendency 

 for a particular sex is transmitted and inherited with the chromatin 

 material of the gamete nuclei, but the expression of this tendency 

 is modified by the conditions under which the zygote develops. 



In view of this quantitative nature of sexuality in plants, one 

 should not expect to find any sharply defined line of demarcation 

 or reliable chemical tests for determining sex. In general, female 

 plants, organs, spores, etc., show a lower intensity of oxidation 

 and a higher reducing power than the male. Accordingly, the fe- 

 male cells are commonly richer in glutathione and poorer in cat- 

 alase than their male counterparts, but there are many exceptions 

 to this rule, as might be expected. 



