82 WEDDEL, ON THE CYSTOLITES 



But this ceases to be the case when the plant is dried. The 

 cystolites in fact do not contract in consequence of the desic- 

 cation like the rest of the tissue of the leaf or stalk, but are 

 in a certain sense protruded externally, and the delicate mem- 

 branous tissue covering them is moulded so exactly upon them 

 that it is difficult when viewing them in this condition, to 

 believe, that they were previously concealed in the thickness 

 of the organ. Many botanists, deceived, under these circum- 

 stances, by their form, which is often linear, their white colour, 

 and especially by the remarkable relief in which they stand, 

 have described them as adnate hairs, others as Malpighian 

 hairs, or lastly as simple tubercles. Gaudichaud was the first 

 to recognise their mineral nature, regarding them, however, as 

 true raphides, an opinion since adopted by several others, but 

 which cannot sustain serious examination. Nevertheless the 

 cystolites thus rendered visible on the exterior by the desic- 

 cation, furnish specific and even generic characters of great 

 value in so natural a family as that of the XJrticacece. Among 

 the genera belonging to this great group, in which these little 

 bodies especially afford good characters, I would here parti- 

 cularly notice the genus Pilea, of which the species at present 

 known amount to more than 100 ; and the genus Elatostema^ 

 which contains nearly 40. Another genus of UrticacecB^ 

 Myi'iocarpa, may be recognised at once, and in the absence of 

 the organs of fructification, by the radiated disposition of the 

 cystolites around the base of the hairs which clothe the upper 

 surface of the leaves. In all these plants the calcareous cor- 

 puscles are, usually, more or less fusiform or linear ; whilst in 

 the greater part of the stinging Urticacece, in the Parietarics, 

 and in the BbhinericB, they are nearly always spheroidal, pre- 

 senting, in the dried plant, the aspect of projecting points, 

 which often give to the leaf a certain asperity, which would 

 be sought for in vain in the living plant. 



In all cases when studying the development of the sphe- 

 roidal cystolites, I have had no difficulty in perceiving the 

 pedicle, although it is sometimes very slender. This tenuity, 

 however, of the suspensory filament is still greater in the 

 linear cystolites ; so great, in fact, that Schacht declares that 

 he has sought for it in vain. Nevertheless there is no doubt of 

 its existence, at any rate in the first period of the development 

 of the corpuscle, for if the cell be viewed from without to 

 within, a minute point will always be observed on its exterior, 

 evidently marking the insertion of the pedicle. It may happen, 

 moreover, that the suspensory filament is eventually com- 

 pletely concealed by the new layers successively added to the 

 body of the concretion, which then appears to be sessile upon 



