42 CLIMBING PLANTS [CHAP. 



as the stems are supported, atrophy presumably 

 follows from disuse as in the animal world. 

 Water having to be carried to great distances, in 

 many cases, as some lianes are from 300 to 400 

 or more feet in length, large vessels are also a 

 prominent feature. These differences which are 

 found between erect stems and those supported, 

 are well seen in Wistaria sinensis when grown as 

 a standard, and conversely on a trellis. The 

 former never sends out long shoots every year, 

 as the latter does, sometimes to a length of 

 30 feet in one season in the United States. 

 An examination of shoots of the same diameter 

 from each sort revealed at once a marked differ- 

 ence. These of the "tree" form, the pith was 

 as 65 to 95 in comparison with the supported 

 one. The wood being in the proportion of 35 

 to 15 ; the number of vessels in that of 30 to 40. 

 The diameter of the largest of the vessels was 3 

 to 3j or 4 in the trained. 



Precisely analogous differences occur between 

 ivy shoots which are self-supporting, and those 

 supported by roots against a wall. Again, similar 

 differences will be found in one and the same 

 shoot of the bittersweet (Solanum Dulcamara) 

 before and after it has secured a support. That 

 the anomalous wood is " caused " by the shoot 

 being supported is obvious from innumerable 

 instances. On the one hand, the wood of a 

 self-supporting stem is symmetrically arranged 



