THE AXGIOSPERMAE : LEAVES 995 



some of these at least have proved, on close investigation, to be true laminate 

 leaves. A well-known case in point is the leaf of certain American species 

 of the umbelliferous genus Eryngium, {e.g., E. agavi folium), which are linear 

 and have parallel venation (see Fig. 946, p. 959). The suggestion that here 

 the leaf consists of a base and a broadened petiole only is not borne out by 

 the ontogeny, which shows that the lamina becomes long and narrow, and 

 that Its pinnae are reduced to long teeth on the leaf margin. There is good 

 reason to believe that the same is true of a number of other apparently 

 phyllodic leaves. 



Fig. 981. — Acacia sp. Shoot showing phyllodes. 



Genuine phyllodes, in which the biological function and the dorsiventral 

 structure of the lamina have been taken over by the petiole or by the leaf base, 

 or a combination of the two, are best known in species of Acacia (Fig. 981). 

 Many species of this genus have the multipinnate, compound leaves which 

 are so frequent among the Leguminosae, but certain species, such as A. 

 longifolia and A. glaiicescens, bear only phyllodes which are simple and mostly 

 somewhat leathery in texture. Their venation is reticulate, like that of a 

 typical dicotyledonous lamina, but one peculiarity marks all these phyllodes, 

 namely, the presence of a strong marginal vein, which runs all round the 

 phyllode (Fig. 982). In most phyllodic Acacias, and in the similar structures 

 in species of Oxalis, such as O. ruscifolia, the seedlings show a striking 

 " recapitulation," that is to say, a series of developmental stages connecting 



