138 



MANUAL OP BOTANY 



as corresponding to a ternate leaf, each lateral lobe of which 

 bears two sporangia, while the central one bears four. It may 

 be considered, indeed, that collateral chorisis is iUnstrated by the 

 compound as compared with the simple leaf. It is evident that, 

 on this hypothesis, collateral chorisis is only a form of branching 

 of the staminal leaf. Other examples of this modification of the 

 typical flower are by some considered to be afforded by the 

 flowers of many species of Hypericum {fig. 265,/, /), in which 

 each bundle of stamens is supposed to arise from the repeated 

 chorisis of a single stamen. Bach bundle may, however, be due 

 to its branching ratlier than to its repeated division. The multi- 

 plication of the stamens of Cratcegus already described (page 136) 

 may be due to this form of chorisis. 



3. Suppression or Abortion. — The suppression or abortion 

 of parts may pertain either to entire wliorls or to one or more 

 parts of a whorl. 



a. Suppression or Abortion of one or more Whorls. — We 

 have already stated that a. complete flower is one which con- 

 tains calyx, corolla, androecium, and gyncecium. When a whorl 

 is suppressed, therefore, the flower necessarily becomes in- 

 complete. This suppression may take place either in the floral 

 envelopes or in the sporophylls. 



Sometimes one whorl of tlie floral envelopes is suppressed, as 

 in Chenopodiuni (fig. 255), in which case the flower is opeiaZotts 



Fig. 255. 



Fig. 256. 



Fig.2b5. Flower of Goosefoot (^Ckenopodium),\jit\i only oue floral envelope 



{monochlamydeous). Fig, 256. Flower of the eoniinou Ash (^Fraxinus)^ 



iu which both floral envelopes are absent (achlamydeous). 



or monochlamydeous ; sometimes both whorls are suppressed, 

 as in the Ash [fig. 256), when the flower is aohlamydeous. 



When from such suppression only one perianth whorl is 

 present, it is usual to speak of it as the calyx, though it may be 



