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A TEXTBOOK OF THEORETICAL BOTANY 



Fig. II02. — Ontogeny of fascicled stamens. A and B, Hypericum androsaemum. C, Cistiis 

 popiilifolius. D, E and F, Philadelphus coronarius. G, Sparmannia africana. H and J, The 

 same, the gynoecium only. Lettering as in Fig. 1099, ^/ = placenta. {After Payer.) 



caused by the local concentration of growth substances, just as in the above- 

 cited examples of local acceleration of growth in certain radial sectors only. 

 It is of great significance in connection w^ith cross-pollination, but its 

 physiology is still obscure. 



THE FLORAL RECEPTACLE 



The axis of the flower, on which the floral organs are borne as lateral 

 organs, is known as the receptacle, or the thalamus. It is a direct 

 continuation of the pedicel and, in flowers with numerous parts, especially 

 spiral flowers, it may be elongated considerably, as in Magnoliaceae, or 

 expanded into a sphere on which the parts are distributed, as in Anno- 

 naceae. When a smaller number of parts is present the receptacle is short 

 and may be no more than a minute cushion. The elongated receptacle has 

 usually been held to be the more primitive form, partly from its occurrence 

 in families regarded as primitive on the basis of their general assemblage of 

 characters, and partly on the ground of its being nearer to the character of 

 a vegetative shoot, with which classical theory compares the flower. 



