LECT. IV.] THE ROOT. TUBERS. J61 



deposite the nutritious fluids in the cells of the 

 parenchyma, take on a retrograde movement, and 

 acquire the functions of absorbents as soon as the 

 tuber begins to vegetate. A knowledge of the dis- 

 tribution of the vascular system of these tubers, 

 and of the manner in which the new tuber is at- 

 tached, with the appearance of the embryon plant 

 at its apex, can be readily obtained by examining 

 a longitudinal section of the base of any Orchis, 

 after the new tuber is formed ; particularly if the 

 plant be injected with a coloured fluid, as has been 

 already described *. From such an examination it 

 is evident, that, however close the attachment of 

 the new and old tubers is in the closely attached 

 tubers, the attaching organ performs a function 

 very similar to that of the umbilical cord of ani- 

 mals ; and resembles in every respect, except in 

 length, the runners which connect the pendulous 



* Vide Plate I. fig. 1. which represents a longitudinal slice 

 of the tuber of the male Orchis, Orchis mascula ; a. the new 

 tuber with its longitudinal vessels, and the intermediate cel- 

 lular texture turgid with nutritious fluid ; b. the old tuber in a 

 half-exhausted state; c. the stem of the plant broken short; 

 d. t\\e plantule, which will form the next year's plant ; e. a kind 

 of sheath over the plantule> which terminates in a membranous 

 cone, and appears to be formed of a doubling of the cuticle 

 of the stem, reflected so as to unite with that of the new- 

 tuber ;f, the point of conjunction of the vessels of the stem and 

 of the old tuber, with those of the plantule and the new tuber ; 

 g. a root produced from the stem* 



VOL. I. M 



