PHANEROGAMIA : BUD ORGANS. 



293 



organs, from which new independent plants develope so soon as they 

 are separated from the parent plants : sometimes this is a specific 

 peculiarity ; as, for instance, the tubers of the species of Amorpho- 

 phallus and other Aracece : sometimes they arise in certain plants 

 particularly readily in consequence of injuries ; as, for instance, in 

 the Gesneriacece on the broken surface, after cutting a leaf nerve 

 at the edge or the point of the leaf. 



These tubercles hold the same relation to the tubers that the bulbels 

 do to bulbs, at least so it appears from what has been already made 

 known upon the subject ; for again, all of the plants belonging here 

 are far too insufficiently known in their development to admit of 

 our defining the relations of the tubercles to the occasionally equally 

 tuberculated stem. 



e. Pseudo-tubers (tuberidia). In some plants a single, frequently 

 an axillary, bud is transformed in a peculiar manner. The paren- 

 chyma of the axis of the bud, which is situated over the vascular 

 surface, suddenly becomes exceedingly expanded in a solid and 

 tuberculated form, by means of the sudden commencement of new 

 formation of cells in isolated groups of cells ; in the axillary bud 

 this only occurs on one side (as in our native Orchidece), since, on 

 the other side, the pressure of the stem prevents such distension. 

 In Aponogeton distachyon, the -thick fleshy cotyledon with the end 

 of the root proves a corresponding obstruction ; hence here, also, 

 the development of the pseudo-tuber is only one-sided. In the 

 Dahlias, on the contrary, the tubercular development is equal on 

 both sides. The mass of cells enters between the base of the 

 cotyledon and the new adven- 

 titious roots, arising, at a very 

 early period, almost imme- 

 diately under the cotyledon, 

 and which, through the form- 

 ation of the pseudo-tubers, be- 

 come gradually removed far 

 away from the cotyledon. 



The process of formation of 

 the pseudo-tubers in the indige- 

 nous Orchidacece, especially Or- 

 chis, Anacamptis, Gymnadenia, 

 Platanthera, and Ophrys, which 

 I have investigated in regard to 

 this point, so far as the species 

 were at my command, is in the 

 highest degree interesting ; I 

 sketch it here, after examples 

 easily to be verified in Orchis 

 Morio (fig. 178.) and latifolia. 

 In the axils of the lower 

 leaves (A, d,) occur axillary 



I7B Orchis Morio. A, Natural size, young plant: a, tuber of the current year; b, scar 

 of that of the former year, cut away ; c, papilla which indicates the formation of the 



u 3 



178 



