478. TEANSMITTED EFFECTS OF LIGHT. Chap. IX 



Experiments similar to the foregoing ones were tried, and wc 

 will give the results as briefly as possible. They are somewhat 

 less conclnsive than in the case of Phalaris, and this may 

 possibly be accounted for by the sensitive zone varying in exten- 

 sion, in a species so long cultivated and variable as the common 

 Oat. Cotyledons a little under three-quarters of an inch in 

 height were selected for trial : six had their summits protected 

 from light by tin-foil caps, •25 inch in depth, and two others by 

 caps -3 inch in depth. Of these 8 cotyledons, five remained 

 upright during 8 hours of exposure, although their lower parts 

 were fully exposed to the light all the time; two were very slightly, 

 and one considerably, bowed towards it. Caps only ■ 2 or ■ 22 inch 

 in depth were placed over 4 other cotyledons, and now only one 

 remained upright, one was slightly, and two considerably bowed 

 to the light. In this and the following cases all the free seedlings 

 in the same pots became greatly bowed to the light. 



Our next trial was made with short lengths of thin and 

 fairly transparent quills ; for glass-tubes of suflcient diameter 

 to go over the cotyledons would have been too heavy. Firstly, 

 the summits of 13 cotyledons were enclosed in unpainted 

 quills, and of these 11 became greatly and 2 slightly bowed 

 to the light ; so that the mere act of enclosure did not prevent 

 the lower part from becoming bowed. Secondly, the summits 

 of 1 1 cotyledons were enclosed in quills ■ 3 inch in length, painted 

 BO as to be impermeable to light; of these, 7 did not be- 

 come at all inclined towards the light, but 3 of them were 

 slightly bent more or less transversely with respect to the line 

 of light, and these might perhaps have been altogether ex- 

 cluded; one alone was slightly bowed towards the light. 

 Painted quills, "25 inch in length, were placed over the summits 

 of 4 other cotyledons ; of these, one alone remained upright, a 

 second was slightly bowed, and the two others as much bowed 

 to the light as the free seedlings in the same pots. These two 

 latter cases, considering that the caps were ■ 25 in length, are 

 inexplicable. 



Lastly, the summits of 8 cotyledons were coated with flexible 

 and highly transparent gold-beaters' skin, and all became as 

 much bowed to the light as the free seedlings. The summits of 

 9 other cotyledons were similarly coated with gold-beaters' skin, 

 which was then painted to a depth of between -25 and "3 inch, 

 so as to be impermeable to light ; of these 5 remained upright, 

 and 4 were well bowed to the light, almost or quite as well as 



