Sex Determination in Phylloxerans and Aphids 241 
they could ever subsequently be caused to produce the sexual 
forms, is not known, but there is nothing that we know opposed to 
such a view. 
Through the courtesy of Prof. W. J. Gies, an analysis was 
made by Dr. W. Berg of the leaves of the rose and of the maple. 
The first analysis was made in June when the young aphids had 
just emerged; the second late in the autumn when the leaves were 
old and the sexual forms had appeared. ‘There is no very great 
difference between the two sets of leaves as the accompanying table 
shows. ‘There is more water in June and more starch in October. 
The ash is also greater in October. ‘These are the only clues that 
the analyses furnish as to differences in the food plants. Of course 
there may be many other substances present that differ in amount 
not brought out by an analysis of this kind. 
ROSE LEAF MAPLE LEAF 
October, 1905. June, 1906. October, 1905. June, 1906. 
| 5 | 
fresh dry | fresh dry 
| 
fresh dry fresh dry 
WAtED eS Sa reccois opts fetter stare 60.25 63.39 — 63.37 SS Paes — 
sHOtal nitKo Pentel #12/-1+1|)02797. | 2-004))|" 0.971 |) 2.645 0.914 | 2.495 | 0.86 ai10 
Etherextract, 05 < aris 's «ie 3-09 7.78 2.238 | 6.114 2.15 5.86 2.10 7.719 
Water soluble reducing 
substances, calculated 
as dextrose............ 212 Prati 2.754| 7-503 | 2.364] 6.453 | 1.102 | 4.050 
Starch (total reducing) 
sugars calculated as 
extnose x tOUOh ar. 6.42 | 16.15 6.63% | 18.06# | 4.081 | 11.14 3-648 | 13.40 
NODS a adoo aud shctoer 3.61 g.085 | 3.069 | 8.215 | 4.775 | 13.10 2.064 | 7.586 
The foregoing discussion is not intended to imply that external 
conditions are not potent factors in the life cycles of species with 
alternating sexual and parthenogenetic reproduction. On the 
contrary, [ am prepared to accept such a view despite the negative 
result of the experiments; but one fact of capital importance has 
been, [ think, overlooked in the interpretation that has been applied 
to the facts. The results show that whatever the conditions are 
that bring about the transformation, the change involves the pro- 
