CHAP. III. UPPER PART OF THE RADICLE. 157 



shire Hero) which has a much -wrinkled tough skin, 

 too large for the included cotyledons ; so that out of 

 30 peas which had been soaked for 24 h. and allowed 

 to germinate on damp sand, the radicles of three were 

 unable to escape, and were crumpled up in a strange 

 manner within the skin ; four other radicles were 

 abruptly bent round the edges of the ruptured skin 

 against which they had pressed. Such abnormalities 

 would probably never, or very rarely, occur with forms 

 developed in a state of nature and subjected to natural 

 selection. One of the four radicles just mentioned in 

 doubling backwards came into contact with the pin 

 by which the pea was fixed to the cork-lid ; and now it 

 bent at right angles round the pin, in a direction quite 

 different from that of the first curvature due to contact 

 with the ruptured skin ; and it thus afforded a good 

 illustration of the tendril-like sensitiveness of the 

 radicle a little above the apex. 



Little squares of the card-like paper were next 

 affixed to radicles of the pea at 4 mm. above the apex, 

 in the same manner as with the bean. Twenty-eight 

 radicles suspended vertically over water were thus 

 treated on different occasions, and 13 of them became 

 curved towards the cards. The greatest degree of 

 curvature amounted to 62 from the perpendicular; 

 but so large an angle was only once formed. On one 

 occasion a slight curvature was perceptible after 5 h. 

 45 m., and it was generally well-marked after 14 h. 

 There can therefore be no doubt that with the pea, 

 irritation from a bit of card attached to one side of the 

 radicle above the apex suffices to induce curvature. 



Squares of card were attached to one side of the tips 

 of 11 radicles within the same jars in which the above 

 trials were made, and five of them became plainly, 

 and one slightly, curved away from this side. Other 



