Influence of External Conditions on Tricotyly. 455 
tricotyls has increased, it is plain that the factors under- 
lying these differences are by no means simple. 
This is further shown by the fact that a repetition of 
the experiments does not always produce the same result. 
Thus in Amarantns spcciosns (1897), and Scrophularia 
nodosa (1898), I was not able to observe any influence 
exerted by the various external conditions on the propor- 
tion of tricotyls, although the experiments were carried 
out on a large scale. I also found that if I sowed sam- 
ples from the same lot of seed in two successive years, 
the mean ratio of tricotyls in the harvest of the two 
cultures was the same, (e. g., Oenothera hirtella, 1898 
and 1899). 
Moreover, unfavorable conditions can sometimes, by 
diminishing the yield, lead to an increase in the per- 
centage values. This is shown by an experiment which 
I made in 1898 with Antirrhinum majits. I covered half 
of my culture with a cage made of fine metal gauze 
painted black, after the plants had developed a stem of 
10 centimeters above the cotyledons. Within the cage 
it was considerably darker than outside, and the plants 
grew very weakly, produced only few branches, and de- 
veloped but a small number of flowers and fruits on the 
terminal spikes. Fertilization was artificial, and all the 
plants were guarded from the visits of insects. The 
yield in the cage was 0.5 cc. per plant, and outside 1 cc. 
per plant. In the former case as many fruits as possible 
were gathered but in the latter the upper flowers of the 
spike were not fertilized. The material used in this 
experiment consisted exclusively of the offspring of a 
single parent of 1897 which had had a value of 14%, 
but tricotylous and dicotylous seedlings were both used, 
each group being planted half within the cage and half 
