76 Prof. C. Morren on the discoid Piths of Plants, 



it is the mode in which the elongation of the branch takes 

 place which tears the pith regularly into discs, whilst obser- 

 vation and the anatomy of the organs prove that these discs 

 are the result of a condition of existence of the pith itself and 

 not of the ligneous apparatus surrounding it. Such is the first 

 conclusion I have come to in this investigation. It will subse- 

 quently serve to prove that this phaenomenon of the separation 

 of the pith into discoid plates is attended with several remark- 

 able changes in the cells of this apparatus, and these changes 

 are in fact the strongest proofs that can be brought to show 

 effectually that the pith is a species oimamillafor the bud; that 

 the modifications which take place in the alimentary cells are 

 the same as those which take place in a cotyledon during ger- 

 mination, but still with conditions often quite different and 

 even inverse. The modifying operation takes place in fact 

 altogether in the cell, to the detriment, in the first place, of 

 its contents, and afterwards of its envelope also. 



These results, and others in addition, which had not been 

 thought of till now, will come out clearly from this investiga- 

 tion ; and the better to convince the reader, I will go into the 

 details themselves, — the analysis of the facts. 



I will first keep to the investigation of Begonia argyrostig- 

 ma, which suits this kind of inquiry extremely well. 



If we take a young stem of this plant, fresh and quite healthy, 

 the diameter of which at the bottom would be a centimetre and 

 more, and diminishing by degrees from the bottom to the top by 

 internodes of 8,7? 3, 1, \ centimetres in length, and we examine 

 its pith, it is found to be of such a size that it occupies y^Q ths of 

 the stalk. Moreover this pith (PI. II. fig. 1.) forms a column 

 channeled by three deep grooves (A, B, C, fig. 1.), and by 

 three slighter grooves alternating with the first [a, b, c, fig. 1.). 

 When the internode is 10 or 9 millimetres in diameter we ob- 

 serve that the pith begins to be perforated with discoid cavi- 

 ties tolerably equidistant, but separated by rather large masses 

 of compact pith {e,f, fig. 2.). But if an internode of 6 or 7 

 millimetres in diameter is taken, we find a pith quite conti- 

 nuous, compact, similar to that of a great number of plants. 

 This change takes place suddenly ; for two successive inter- 

 nodes, the one of 7 millimetres in diameter, the other of 9, 



