74 DUDLEY MEMORIAL VOLUME 



female prothalli. These are very surprising, but what I have recorded above 

 for Pteris aquilina sowed X, 11, 1911, is equally true of those started on XI, 

 13, 1911, allowing for the slight and decreasing differences due to age, and 

 of both sets of cultures of Gymno gramme triangularis. How can one account 

 for these differences? The cultures were sowed all together, the culture solu- 

 tion, the tiles and the dishes had all been treated exactly alike and together ; 

 no selections were made at any time. Some of the cultures were put on the 

 turn-tables at once after sowing and the remainder were placed on the shelf by 

 them. They were thereupon marked. Almost from the moment when the 

 dry spores touched the moist tile they began, either to remain still, or to turn, 

 with the tile on which they had fallen. And so they remained night and day, 

 the diffused sunlight from the window falling through a white Holland 

 shade nearly horizontally upon them by day, darkness enveloping them at 

 night (for I very seldom use artificial light in the room where the multiple 

 clinostat is), turning night and day or staying motionless, according to their 

 position; watered from time to time with fresh Knopp's solution when nec- 

 essary, equally warmed and similarly treated in every respect, so far as I 

 can see, except that in one respect they are not similarly lighted. The light 

 is the same in composition, intensity and duration, not in direction. This dif- 

 ference alone is accompanied by the differences in the vegetative and the re- 

 productive parts above described. 



It may be easier to gain some insight into this problem, into the reasons 

 or causes of these differences, if we consider the vegetative and the repro- 

 ductive parts separately. Acting on this principle, I proceeded to experiment 

 upon young flowering plants grown from the seed. 



SEEDLINGS OF MUSTARD AND OF WHEAT. 



Seedlings of white mustard (Sinapis alba) and of wheat were sowed on 

 sterilized greenhouse soil in 2-inch porous flower pots. I selected these 

 plants because of the promptness with which they germinate and the vigor 

 with which they grow, for a time at least, under laboratory conditions, and 

 because the early growth of the one (mustard) is mainly hypocotyledonary 

 and at the expense of food made by the seedling as well as drawn from the 

 seed, whereas the growth of the other (wheat) is mainly epicotyledonary and 

 the seedling, though well fed, is not self-nourishing for some time. Recalling 

 the well known phototropism of these two seedlings, I thought that by ex- 

 posing the two sets, one on the shelf and one on the turn-tables, to the same 

 light, I could ascertain whether there were any greater stimulus to growth 

 for the one set of plants or the other, whether if an adjustment as to position 

 between light and darkness — that is, between more and less light — cannot be 

 attained, growth will be more rapid than where a plant is able to attain a 



