162 CONSERVATIVE ORGANS. [LECT. IV. 



tubers with the parent plant. In fact, the attach- 

 ment, when the tuber is viewed in its natural state, 

 appears much shorter than it actually is, owing to 

 the shortness of the collar of 

 the stem: but circumstances 

 occasionally occur which 

 lengthen the organ, so as 

 to give it the real character 

 of a runner, and render the 

 new tuber pendulous (fig. 

 w) *. 



If we take the Potatoe to 

 exemplify the organization of 

 the tubers of Dicotyledons, we shall find that 

 they resemble, in an equal degree, the stems 

 of the tribe. When a tuber of this plant is cut, 

 either transversely or longitudinally, it appears 

 evidently to be composed of two distinct parts ; 

 one of which is internal and cellular, somewhat 

 like the pith or central part of the stern of the 

 plant, and surrounded on every side by the other, 

 which is cellular also but more dense, and bor- 

 dered with a complicated system of vessels, 

 branches from which stretch into the pith ; and 

 that it has a close affinity to the cortical part of 

 the stem. 



* The plant from which this figure was drawn was raised in 

 a common garden pot, with the old tuber very near the surface. 

 a. The old tuber ; b. the new tuber ; e. the attaching process 

 extended so as to assume the form of a runner. 



