REVERSION TO THE JUVENILE FORM 



the 



spreading stalked flat primary leaves instead of the adpressed scale- 

 like ones (Fig. 106). In the Cacteae reversion- 

 shoots often appear, but the cause of their 

 appearance has not yet been experimentally 

 investigated 1 . The like holds good for many 

 other plants. 



We may say generally that the reversion- 

 shoots appear at definite places and usually near 

 the base of the plant ; thus many juvenile shoots 

 appear on the lower part often covering the stem 

 for several yards of old 

 plants of Eucalyptus in 

 Italy. The same is the 

 case in Cupressineae, for 

 example, in old plants of 

 Callitris, also in Colletia 

 cruciata-, and others. From 

 what has been said above 

 we can understand the ap- 

 pearance of the reversion- 

 shoots at the base of plants 

 as, on the one hand, they 

 will be least influenced in 

 this position by the other 

 form of shoot, and, on the 

 other hand, the base can 

 retain from the earliest ger- 

 mination the character of 

 the juvenile form. 



The fact that in young 



plants of Cupressineae injuries by frost, parasites, 

 wounding of the roots, and similar causes induce 

 the development of branches having the juvenile 

 form , whilst in normal plants these would have 

 taken that of the adult, conforms with what has 

 just been said. The frequent appearance of 

 reversion-shoots at the base of many plants might 

 find a teleological explanation in the developing 

 shoots having there similar external conditions to 

 those which the seedling finds when it shoots 



FIG. 11)6. Veronica lyco- 

 podioides. The lower part of 

 the shoot shows the entire 

 scale-like adpressed leaves 

 characteristic of the species, 

 in the upper part are the much 

 larger pinnatilid spreading 

 stalked ' reversion-leaves.' 



FIG. 105. Acacia verticillata. 

 Young plant which, after reaching a 

 stage in which it formed needle-like 

 'phyllodes,' has produced on some 

 twigs the bipinnate juvenile form of 

 leaf. 



1 See what was said about Phyllocactus on page 169. 



2 See Fig. 8 in my ' Pflanzenbiologische Schilderungen,' i. 

 11 Beyerinck, in Botan. Zeitung, 1890, p. 539. 



