Sex Determination in Phylloxerans and Aphids 329 
In the dioecious mosses the important experiments of Elie and 
Emile Marchal show interesting sex relations. In Ceratodon 
purpureus, Barbula unguiculata and Bryum argenteum each pro- 
tonema gives rise to male or to female “flowers,” i. e., the sexes are 
separate. When the odspore is fertilized by an antherozooid the 
resulting sporophyte produces spores which produce again the 
male or the female protonema. The Marchals found by sowing 
spores from single capsules that some of the spores produce male 
protonema, others female. In current phraseology this means 
that the fertilized odspore contains both sexes combined and these 
are “separated” again, in the spores or, put in another way, the 
factors that produce the male and the female sex cells are both 
present in the odspore generation and are separated when the 
spores are formd. 
The experiments prove that the spores are not hermaphro- 
ditic, i. e., capable of giving rise to male and female buds on the 
same protonema; they leave open the question whether the sex is 
predetermined in the spore or whether the protonema gradually 
develops one or the other sex during its life in response to external 
conditions. 
This possibility was tested by cutting off pieces from a proto- 
nema of known sex and raising them under very diverse conditions. 
Such pieces regenerate a new protonema. These secondary pro- 
tonemata are always of the same sex as that of the original proto- 
nema. The evidence is still not final for it might be claimed that 
sex once determined at a critical stage by external conditions is 
irreversible in later stages, until the critical stage is again reached. 
In a second paper the Marchals give some further experiments. 
Tt has long been known that the tissues of the sporophyte will pro- 
duce a protonemaif separated from the parent plant, and put under 
favorable conditions. Since these tissues result directly from the 
fertilized egg, they contain the full number of chromosomes, and, 
theoretically at least, also the double sex potentiality. The results 
show in fact that the same protonema produces both male and 
female flowers. The details are worth careful scrutiny. The 
frst formed flowers were male in large excess, I: 25.8. Later 
1:8.7 and finally 1: 7.8. This predominance of male elements 
