LECT. VIII.] STRUCTURE OF LIGNEOUS ROOTS. 411 



perforated with absorbing pores: such is their 

 earliest character in every dicotyledonous root I 

 have examined. At this period they are productions 

 of the bark only of the radicle ; but a few ligne- 

 ous vessels soon shoot into their centre, and they 

 begin to lengthen (see Plate 8, fig. A. B*); always, 

 however, retaining a clubbed appearance at the 

 apex (see b. b. marginal cut). They shrivel up in a 

 few seconds after the root is taken out of the 

 earth, and then appear as represented at c. c. 

 (marginal cut) ; but so great are their absorbent 

 powers, that, when perfectly dry, if thrown into 

 water, they expand again in a few seconds to their 

 original size. The minuteness of these pores ren- 

 ders it impossible, even by the aid of the most 

 powerful glasses, to obtain a knowledge of their 

 structure ; and although the fibril shrivels so 

 quickly, yet the smallness of the parts prevents 

 us from determining whether this shrivelling be the 

 consequence of exhalation, or of the fluid being 

 carried forwards into the radicle. Whatever may 

 be the structure of these pores, they are evidently 



* Fig. 1 A. represents, greatly magnified, the entire fibril 

 soon after it begins to lengthen ; the dark shade a. in the centre 

 being produced by the ligneous vessels, which are more opaque 

 than the cellular matter; b. is the real size of the fibril. Fig. 

 1, B. is a transverse section of the same fibril; a. the vessels, 

 b. c. the cellular matter filled with transparent granules, which 

 are much more numerous in the exterior circle b. ; d. the real 

 size of the section. 



