28 BOTANY 



and has more character ; while the other tissues seem 

 to group themselves round it. It is to the plant's 

 body what the bony skeleton and the arterial system 

 combined are to the animal. It is thus not surprising 

 that most work on plant anatomy treats principally 

 of the woody cylinder. 



What we have considered so far has been the vascular 

 arrangement in the highest and most important family 

 of plants, the flowering plants. In the lower families, 

 both living and extinct, there are many other types 

 of arrangement. The study of anatomy, therefore, 

 bears on systematic botany, for the constant internal 

 characters of the organs form reliable criteria for the 

 separation of the different groups. 



The outstanding features in the anatomy of the other 

 principal groups of plants is as follows : 



The Gymnosperms (the pine-tree group) have a general 

 structure similar to that of the Dicotyledons. Their 

 wood differs, however, in the character of its uniform 

 cells and in the pitting of their walls a point we have 

 not yet considered. They have a hollow primary 

 cylinder with secondary zones of wood, quite similar 

 to those in the flowering plants. 



The Ferns, as they are now represented by the living 

 species, are very different in their stem anatomy from 

 these higher plants. In the first place, the primary 

 organisation of their stems shows great variation in 

 type in the different species. Yet the majority agree 

 in having a number of separate strands, each organised 

 like that of the root of the higher plants in so far as it 

 has the wood in the centre with the bast surrounding 

 it, and that each such strand is shut off from the sur- 

 rounding parenchyma by a specially organised sheath 

 the epidermis. In a few ferns a single hollow cylinder 



