IN ANGIOSPERMAE. XEROPHILOUS PLANTS 



169 



reduced lateral shoots standing in the axil of the leaves. In many plants 

 these tufts of spines are arranged on vertical ribs of the stem and this 

 may be designated the ' Cereus-form.' From this form diverges in a very 

 strikino- manner that which has a flat leaf-like shoot-axis as we see in 



o 



many species of Epiphyllum, Rhipsalis, and Phyllocactus l , and which 

 may be termed the Phyllocactus-form.' If the history of germination 

 be followed it will be found that the seedling plants have mostly a form 

 which is like that I have described as the ' typical ' configuration, although 



FIG. 103. Phyllocactus phyllanthoides. Seedling plant. The shoots are at first man)' angled and Cereus-like, 

 but in the youngest shoot the number of the angles is reduced to three ; the angles are \ving-like. Later only 

 two angles are found. 



in different degrees in the different species, and we can follow in the 

 seedlings how a transformation of form is brought about. Fig. 103 

 represents a seedling plant of Phyllocactus phyllanthoides which possesses 

 a tetragonal shoot-axis beset with tufts of thorns on the ribs, and has 

 quite the appearance of a Cereus. As the plant grows only two of the 

 ribs remain, the shoot-axis becomes greatly flattened, and out of what 

 was a ' Cereus-form ' there is developed the apparently far removed ' Phyllo- 

 cactus-form.' Other species also of the same genus show in germination 



1 Phyllocactus is only distinguished from Cereus by its habit. 



