336 Origin of Each Species Considered Separately. 



In late autumn there appears on the inner side of the 

 sclerenchym ring a thin layer of cork which must of 

 course have been laid down much earlier and possibly 



stands in some causal re- 

 lation to the external 

 characters of the plant. 

 This species is char- 

 acterized by an apparent 

 inability to stretch its 

 stem — so to speak — 

 which is particularly no- 

 ticeable in weak plants. 

 This character is, in all 

 probability, due to the 

 weakness of the bast- 

 fibres we have just de- 

 scribed. Fig. 70 repre- 

 sents a young plant 

 grown in a pot, about the 

 beginning of July, and 

 illustrates this feature 

 very well. The stem is 

 not straight but bent in 

 a zig-zag fashion; in 

 such a way that the 

 bends occur at the nodes 

 and the leaves are in- 

 serted in their outer con- 

 vex sides. These bends 

 do not straighten out 

 with subsequent growth ; in fact they are often even more 

 pronounced on the fruiting plants. The stronger the 

 stem is, the less is this character developed; but I have, 



Fig. 70. Oenothera rnhrinervis. — 

 Young annual plant, 30 cm. high, 

 about V3 natural size. To show the 

 zigzag course of the brittle stem. 



