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A TEXTBOOK OF THEORETICAL BOTANY 



Fig. 1125. — Saxifraga gramdato. Inflorescence diagrams of two different races showing 

 the different distribution of right-handed and left-handed flowers in the two cases. 

 {After Goebel.) 



There are two other conspicuous departures from the quincuncial order. 

 The first is the vexillate form characteristic of Papihonaceae (Fig. 1126). 

 The standard petal is part 4, but instead of being internal, its superior 

 vigour of growth renders it entirely external. The second is the cochleate, 

 characteristic of the type of scrophulariaceous flowers called " personate " 

 (see p. 1 155). Here the second part, which is the anterior petal of the flower, 

 is delayed in growth and is internal to both its neighbours. 



Fig. II 26. — Diagrams of aestivation. A, Vexillate. 

 B, Cochleate. 



Analogous differences occur in the aestivation of monocotyledonous 

 flowers, with a \ phyllotaxy, but in this class, with the smaller number of 

 parts in a whorl, it is not uncommon for the parts to be entirely separated, 

 so that no question of overlapping arises. 



The act of flowering is called anthesis. The initiation of flowers has 

 sometimes been attributed to " flower-building substances ", but if by this 

 is meant the action of peculiar compounds which specifically build floral 

 tissues and no others, then there is no evidence of their existence. What is 

 more probable is that under certain conditions the physiological system of 



