THE MORPHOLOGICAL COMPOSITION OF PLANTS. 



57 



bame time that the incurved edges of the foliar surfaces 

 united. The arrangements of the tubular axis and its ap- 

 pendages, thus resulting, are still more iastructive than those 

 of the soKd axis. For while, even more clearly than ia the 

 Dcmdrobium, we see at the point b, a continuity of structure 

 between the substance of the axis below the node, and the 

 substance of the sheath above the node ; we see that this 

 sheath, instead of having its edges united as in Bendrohium, 

 has them simply overlapping, so as to form an iacomplete 

 hollow cyUnder which may be taken off and unrolled; 



and we see that were the overlapping edges of this sheath, 

 united all the way from the node a to the node b, it would 

 constitute a tubular axis, like that which precedes it or like 

 that which it includes. And then, giving an unexpected 

 conclusiveness to the argument, it turns out that in one 

 family of grasses, the overlapping edges of the sheaths do 

 unite : thus furnishing us with a demonstration that tubular 

 structures are produced by the iucurving and joining oi 

 foliar surfaces ; and that so, hollow axes may be interpreted 

 as above, without making any assumption unwarranted by 

 fact. One further correspondence between the 



type thus ideally constructed, and the endogenous type, must 

 oe noted. If, as already pointed out, the transverse growth of 



