STUDIES IN THE DEVELOPMENT OF THE PIPERACEAE 731 
time of formation of the sporophylls, when a separation of the 
sexes is evident. Here, as in the case of - the gametophyte of the 
fern, the male influence or substance, seems dominant at first, 
as is evidenced by the earher origin of the microsporophylls in 
most instances. These angiosperms differ in this respect from 
those Selaginellas with basal, (i.e. older), megasporophylls and 
terminal microsporophylls, though they resemble these selagi- 
nellas in having both megasporangia and microsporangia on 
the same axis. The monoecious Araceae, among angiosperrr s, 
also offer an example, or, at least, evidence, of the earlier dom- 
inance, of femaleness, in the usually basal position of the female 
flowers, on the spadix. Cases have also been noticed by Correns 
('08), in Satureia, and by Strasburger ('09-) in Mercurialis, where 
purely female flowers are the first to develop in the inflorescences 
of these plants, the stamens not developing until much later. 
We now come to the second part of our question, namely, the 
cause of the segregation of the sexes at the particular point where 
it does occur. 
Experimental work on a number of plants has shown pretty 
clearly that the distribution of nutrient substances in the plant, 
together with the external conditions affecting the nutrition of 
the plant as a whole, are among the important factors concerned 
in the expression or suppression of certain organ-building tend- 
encies in plants. We may recall in this connection only such of 
this work as bears on the causes of development of the reproduc- 
tive organs. 
Klebs has shown that the development or non-development of 
the sexual reproductive organs of Vaucheria, som^e other algae, 
and certain seed plants can be determined by changing such 
external factors as the osmotic or chemical character of the nutri- 
ent solution, or of the light or temperature affecting the plant. 
These facts strongl}' suggest that such factors may also determiine 
which sex may be assumed by any individual in dioecious plants. 
Among higher plants, such as ferns and Equisetum, n^any ob- 
servers have asserted that the smaller, poorly nourished gameto- 
phytes are always m.ale. In view of the fact that the antheridia 
appear on normal prothallia before the archegonia, the persistent 
