64 TRANSACTIONS OF THE [Sess. lxxvi. 



side of the leaf ; also the axillary branches on the creeping 

 shoots of some of the terrestrial Utricularise arise on the 

 side of the leaf furthest away from the growing-point. 1 



In other respects it may be assumed that the position of 

 the male capitula of Ambrosia means the same thing as the 

 torsion (entirely brought about by their weight) of the male 

 inflorescences of Corylus, Alnus, Juglans, or the torsion of 

 the anther of grasses : by this means the shaking out of the 

 pollen is facilitated in all these anemophilous plants. 



Returning now to the morphological question, one might, 

 in arriving at a decision, also take the anatomical facts 

 into account. If (a) (fig. 1) represents the bract of the 

 capitulum, then one might expect that the normal orienta- 

 tion would be shown in the constitution of the vascular 

 bundle, phloem on the lower side, xylem on the upper. 

 Of course, I do not regard the anatomical conditions as 

 decisive, since, in my opinion, these are determined by the 

 morphological, not the reverse. In the present instance 

 this would mean that, in the event of a relatively limited 

 development and retardation in time on the part of the 

 bract in comparison with the axillary shoot, it appears 

 quite natural that the former (the bract) should be pro- 

 vided with its vascular system from the latter (the shoot). 

 This being so, one expects the xylem to be uppermost, with 

 the phloem underneath. 



The conditions actually existing are briefly as follows : 

 The thin, much-flattened peduncle of the capitulum contains 

 two vascular bundles (rarely three) ; the phloem-groups of 

 these are set towards the narrow margins, and the xylems 

 are turned towards one another and somewhat obliquely 

 downwards (fig. 3). This anatomical structure is interest- 

 ing because unusual in a shoot-axis. 



A certain biassed school of anatomists assumes that 

 shoots are distinguished from leaves by their anatomical 

 structure, particularly in the arrangement of the vascular 

 bundles. The shoot of the capitulum of Ambrosia does 

 not differ in structure from many leaf -stalks, except that 

 in the latter the xylem of the vascular bundle is directed 

 upwards. 



1 K. Goebel, Utricularia ("Annal. du jardin botan. de Buitenzorg," 

 vii. 1889). 



