226 



PRINCIPLES OF PLANT-TERATOLOGY. 



Buddleia; that both, however, represent imperfectly- 

 formed double leaves is, on comparative grounds, fairly 

 certain. In another of De Vries' snapdragon seedlings 

 the double plumular leaf was of another type, being 

 flat and expanded and only very slightly infolded at 

 the base ; it had two distinct midribs (PI. XXII, 

 fig. 6 b). This is comparable to the cases of Caly- 

 ccmthus and Calendula cited by Klein, where a double 

 leaf, occurring in the axil of another leaf, was formed 

 by the lateral union of the two leaves of the first 

 pair of the axillary shoot, this being itself sup- 

 pressed.* Klein also figures leaves, usually double, 

 but in one case triple, of Philadelphus and Calycanthus, 

 which were terminal to leafy shoots, and due to the 

 union, along one of their two margins only, of two or 

 three leaves of the whorl. 



In a mature shoot of the horehound (Marmbium 

 vulgare) the uppermost pair of opposite leaves was 

 represented by a terminal double leaf (PI. XXII, fig. 4). 

 On examining this structure anatomically it was found 

 that the collateral vascular bundles constituting the 

 midribs of each opposite side of the cup formed, along 

 with all the confluent lateral veins, lower down in the 

 cup-stalk, a vascular cylinder precisely like that of a 

 stem. In this case there was not the slightest sign of 

 the real stem-apex. 



All the cases above described are genuinely terminal 

 foliage-leaves ; every one of them, although some are 

 double in their origin, are single organs terminating 

 the axis. 



Bracts. 



An umbel of (Enanthe crocata had a fasciated 

 primary ray, branching above. Bracts appeared at 

 the point of branching, doubtless due to the simulation 

 by the fasciated portion of the peduncle of the 

 inflorescence. 



# Cf. origin of ovuliferous scale in Abietinese. 



