[ 441 J 



XXVI. 



ON THE VEGETATIVE ORG-ANS OF VANDA TERES. By 

 HENRY H. DIXON, B.A., Assistant to the Professor of 

 Botany, Trinity College, Dublin„ (Plates XI., XII., XIII.,, 

 and XIV.) 



[Eead February 26, 1894.-] 



[communicated by e. peeceval weight, M.D.] 



The following Paper is an attempt to give an account of some 

 points of interest in the anatomy of the vegetative organs of Yanda 

 teres which have been worked out in the Botanical Laboratory of 

 Trinity College. 



In its native country this orchid is described as growing to a 

 length of several feet, epiphytic on various trees. The leaves are 

 composed of a cylindrical lamina 10-15 cm. long, attached to a tubular 

 petiole, measuring 2*5-4 cm., which surrounds the stem, fitting it closely, 

 and which completely, or nearly completely, covers the internode, 

 above the insertion of the leaf ; so that usually none of the stem of an 

 uninjured plant is to be seen ; or, if any is visible, it is only the top 

 of the older internodes. The plant climbs over the supporting trees 

 by means of its adventitious roots, which arise in the stem, just above 

 the insei'tion of the leaves. Unless the direct growth of the main 

 stem is checked by injury to the apex, Vanda teres does not frequently 

 branch, its lateral branching being almost confined to the production 

 of flower-bearing shoots. The development of these flower-stems, 

 and of its lateral branches in general, is very peculiar. 



At the base of each internode there is a more or less marked 

 swelling, which is the axillary bud, as may be determined by 

 removing the subtending leaf. This swelling is opposite the lamina 

 of the leaf below the subtending leaf, and on the level of the point 

 of junction between the lamina and petiole of the former. When an 

 axillary bud starts into growth, it first gradually bulges out the base 

 of the petiole of its subtending leaf, and finally, instead of growing 

 up in its axil, it ruptures it and pierces through it. After it emerges 

 from the opening it has forced through the petiole, it turns upwards 



