234 THE PATH OF DEGENERATIVE EVOLUTION 



the primitive type. We cannot decide between the 

 alternatives. 



2. Branches of Colletia cruciata, Crataegus, Vicia 

 Faba, etc. Some cases, however, point clearly to 

 a renewed development of rudimentary organs. 

 Here are some examples. (See also, further on, 

 page 244 on hybrid individuals of Pentstemon.) 



Colletia cruciata, (fig. 72) in the normal adult 

 condition bears large flattened branches, which 

 serve for assimilation and possess only very rudi- 

 mentary leaves. Sometimes, however, the plant may 

 give rise to more slender branches with normal 

 assimilating leaves. These branches and leaves are 

 probably the reappearance of the ancestral condition. 



Wild pear and apple trees produce small lateral 

 branches which are transformed into spines. These 

 thorns have evidently arisen from normal lateral 

 branches which originally bore leaves. In the 

 cultivated varieties these lateral branches have 

 resumed the leaf-bearing habit. 



In the hawthorn (Crataegus) the lateral branches 

 are similarly modified into spines. None the less, 

 while these spines are still young they may be 

 artificially stimulated to produce leaves by cutting 

 the principal stem. 



The branches of Vicia faba bear low down a set 

 of rudimentary leaves. If the main stem be lopped 

 while still quite young, the usually rudimentary 

 leaves grow to the normal size. 1 



1 Goebel, Beitrage zur Morphologie und Physiologic des Blattes. 

 Bot. Zeit, 1880. 



