Prof. C. Morren o% the discoid Piths of Plants. 79 



rather separated into as many discs as possible, in order that 

 each one might touch its neighbour, and that there might be 

 the greater number of lenticular cavities between them. What 

 is most astonishing is the regularity of this arrangement, as 

 may be seen in figure 3. 



It now became a subject of interest to examine the intimate 

 structure of these discs. And at first, upon taking them off 

 the stalk, in the form of membranes of a shining reddish- 

 brown and very dry, I was struck with the great number of 

 brilliant points which were detached from their surface and 

 powdered the stage of the microscope. These brilliant points 

 were in fact a vast quantity oi octohedral crystals [f, fig. 5.) 

 similar to those I had so clearly seen scattered in the young 

 pith, but much more voluminous ; and others were dodeca- 

 hedral crystals, some of which having their tops truncated, 

 thus presented fourteen facets (e, fig. 5.). These crystals 

 lined, principally the surfaces of the pith, all along the stem, 

 rather than the transverse discs. 



The latter were formed of cells two or three times larger 

 than those of the young pith, and nevertheless the stalk upon 

 w^hich my observations were made, only measured twelve mil- 

 lemetres in diameter, that is to say, two millemetres more than 

 the stem where the pith, still young, was not yet formed of 

 discs ; — a proof that it is not the augmentation of the stem 

 w^hich by pulling the cells had caused their increase in diame- 

 ter ; a proof, moreover, that this development of the cells has 

 its origin in the cells themselves, and in the changes which 

 they undergo. 



What characterized these cells was the numerous folds of 

 their membrane (figs. 5. and 6.) ; which generally proceeded 

 from central points whence they radiated (fig. 6.). The water 

 of vegetation had disappeared, some few globules (fig. 5 Cy 

 fig. 6 b) still remained here and there, but in general the or- 

 ganic utricular element was dry and empty ; it was dead and 

 withered. 



In resuming these observations on the discoid pith of 

 the Begonia argyrostigma, we find that the formation of the 

 discs is attended with a phasnomenon w^hich takes place in 

 the cellular tissue itself, and which is connected with the me- 



