Dixon — On the Vegetative Organs of Vanda teres. 445 



pierces through the leaf. In fact, the axillary bud is so entirely 

 changed in position relative to the main axis that the direction of 

 its growth, instead of forming an acute angle with the main axis^ is 

 displaced by the unequal growth of its parts, into a horizontal plane, 

 i.e. perpendicular to the primary axis, with its apex pointing towards 

 the latter. This vigorous and unequal growth takes place in that 

 part of the lateral shoot which is below the insertion of its first leaf. 

 In this part the growth of the lower side is much greater than that of 

 the upper, and so pushes what is morphologically the inferior side 

 of the bud into a superior position, turning the base of the lateral 

 axis outwards, and its apex inwards towards the mother axis. 

 During this process the subtending leaf is ruptured, while the part of 

 the lateral shoot which is below the first leaf, and is turned outward, 

 swells and becomes the tuber which replaces the old plant next season. 

 The rest of the elongated lower part of the lateral axis persists for 

 some time as a connection between the old and the new tuber. 



This account of Irmisch of the development of the tubers of Her- 

 minium monarchis is, so far as I know, the only description of the 

 mode of branching which is so frequent among the orchids ; and 

 indeed it is doubtful whether, in this case, it is really the lateral 

 bud itself that pierces the leaf. Irmisch himself regards the tubers in 

 H. monarchis as swollen roots, and accordingly we may regard the 

 leaf as broken through by an adventitious root developed from the 

 base of an axillary bud which is formed in order to give rise to a 

 young independent plant. In this way the root not only breaks 

 through the outer tissues of the organ from which it is developed 

 but also the subtending leaf. Besides in many orchids, I have also 

 observed this rupturing of the subtending leaf by the axillary bud in 

 several species of Bambusa ; also in some bulbs of Syacinthus nutans 

 which had been accidentally displaced in the soil, so that their axis 

 lay horizontally, the axillary buds developed and pierced through the 

 fleshy leaves of the bulb. 



Among the orchids not adopting this method Fernandezia elegans 

 is peculiar. In it the bud arising in the axil of an equitant leaf, 

 which sheaths the stem closely as it develops, turns obliquely round 

 the stem, so that when it emerges from the petiole it is situated 

 opposite the lamina of subtending leaf. 



Stetjctuke of the Stem in Vajstda teees. 



If we examine the transverse section of a well-developed inter- 

 node, we see that the bundles lie in an annular space, separated 



