444 Proceedings of the Royal Irish Academy. 



Dendrobium, and of other genera of orcliids. I have examined B. war- 

 dianan^ B. clirysanthum, and B. Pierardi. In these orchids the buds 

 which form the inflorescences are developed in the axils of the leaves 

 along the fleshy stems. The petioles form thin tubes, coating the 

 stem closely, and on the older stem are of a membraneous texture. 

 The laminae of the leaves are flat, and deciduous from the petiole. 

 The inflorescence may develop while the lamina is still attached, e.g. 

 B. chrysanthum, or after it has fallen away, e.g. B. Pierardi. In both 

 cases the bud which develops breaks its way through the petiole. 

 PI. XI., fig. 2, represents a lateral bud of B. chrysanthum, before it has 

 started into growth, in longitudinal section. In this section on some 

 of the leaves are to be seen top-shaped glands, which have secreted so 

 vigorously that in some places the spaces between the leaves are com- 

 pletely filled up with a dark substance. In B. Pierardi this substance 

 glues the membraneous petiole to the stem, so that even in the thinnest 

 transverse sections it adheres to the stem. In this last case it seems 

 certain that the axillary bud in breaking its way through the petiole 

 meets with less resistance than if it were to grow up in the axil. 



The apex of these Dendrobia is by no means so completely shut in 

 by the individual leaves as that of V. teres. However, the great number 

 of leaves which arch over it, and fold across one another, render 

 the contrivance adopted by V. teres, which is eminently suitable where 

 there are but few leaves to cover the apex unnecessary. 



The curious habit of the bud piercing through the base of the 

 leaves which occurs in these orchids naturally reminds one of the 

 similar behaviour of the lateral branches of the Ec[uisetaceae, and 

 indeed a casual observer might as easily consider the branches of Vanda 

 teres, &c., endogenous as those of the Equiseta. 



Goebel (Pflanzen biologische Schilderungun, Th. i. p. 106) compares 

 the development of the lateral shoots of Rhipsalis paradoxa to that of 

 the Equiseta. In this plant the subtending leaf fuses with the inter- 

 node above the axillary bud, and the bud, like that of the orchids 

 just described has to penetrate the petiole in developing. Rhipsalis 

 paradoxa has, like V. teres, to contend against prolonged droughts. 



A somewhat similar development of axillary buds is described by 

 Thilo Irmisch ("Beitrage zur Biologic und Morphologie der Orchi- 

 deen." Leipzig, 1853). The axillary bud of Herminum monarchis, 

 during its development into the tuber, which produces the new plant, 

 breaks through the base of the subtending leaf. This it does only 

 after a very curious displacement of its parts, so that it appears that 

 it is not the bud itself, certainly not its apex, but rather a root which 



