SECT. I. UTRICLES. 340 



the bags or bladders of the cellular integument and 

 pith, and of the pulp of the leaf and fruit, but also 

 the very fabric of the divergent layers themselves, 

 assuming a peculiarity of aspect according to the 

 degree of compression they sustain from other 

 parts ; or according to the degree of induration 

 they may have undergone, ascending progressively 

 from the succulent texture of the pulp and pith to 

 that of the firm and perfect wood. 



The structure of the utricles of the tree is also In trees, 

 said to be different from that of the utricles of the 

 herb, the former being composed of a single mem- 

 brane, and the latter of a double membrane. Sene- 

 bier is, however, of opinion that they consist of a 

 double membrane in both cases, though not so con- 

 spicuous in the one case as in the other, owing to 

 the more compact and condensed texture of the 

 wood. But of this I can say nothing from any 

 observations of my own, having never been able to 

 satisfy myself of the existence of the double mem- 

 brane in either case. 



However, they are all mutually connected with one United to 

 another and also with the other vessels of the plant ; t 

 which double union is rendered evident by means of tubes " 

 coloured injections, or rather by means of the ab- 

 sorption of coloured infusions, from which the 

 utricles, as well as the longitudinal tubes, always re- 

 ceive a tinge. But in the petals, stamens, and 

 pistils, they do not seem to be connected with the 

 longitudinal vessels as in the other parts of the 



