THE INFLORESCENCE, AND THE FLOWER 



^37 



abortion of one or other of the essential parts. A good example is 

 seen in Lychnis dioica (Fig. 184). The Fink family to which it belongs 

 have usually hermaphrodite flowers ; but here the species is dioecious, 

 which means that some plants have only staminate others only 

 pistillate flowers. An examination of each of them shows that in the 

 staminate flowers an abortive gynoecium occupies the centre (iv.) ; in 

 the pistillate flowers ten staminodes, or abortive stamens, surround the 

 base of the ovary (li.). Since these parts correspond in position to the 

 parts normally present in allied plants, they indicate that L. dioica is 

 dioecious by abortion. There is evidence that this form of meiogeny 

 has been of frequent occurrence in the evolution of Flowering Plants. 



Such results are sometimes seen in extreme form, and nowhere better than in 

 the Spurge. Comparison indicates that the Euphorbiaceae are related to the 

 Geranium Family, which are tjipically hermaphrodite. Some of the Spurge 

 Family (e.g. Andrachne, Phyllanthiis) have calyx and corolla represented, but 

 only stamens or carpels, never both. Others show steps of further reduction of 

 floral structure, till in Euphorbia itself the staminate and pistillate flowers reach 

 a very simple condition. The former appear as a single stamen, with a nng 

 half way up its stalk. This represents the abortive perianth. The pistillate 

 flower consists of three coherent carpels, vnth. a rim below, which represents 

 again the abortive perianth (Fig. 169, p. 222). The facts justify the con- 

 clusion that there is here a very advanced 

 state of meiomery. Such extreme reduction 

 is usually connected with a close crowding 

 of numerous flowers in an aggregated inflo- 

 rescence. 



(vi) Various development of the floral 

 axis or receptacle accounts for very con- 

 siderable differences of floral construc- 

 tion. As a rule the parts of the flower 

 are closely packed upon the shortened 

 and distended axis. In primitive types, 

 such as the Buttercup, or Mousetail 

 (Fig. 185), the receptacle is conical, and 

 the sepals, petals, stamens and carpels 

 succeed one another upon it without any 

 interval. Where the stamens are thus 

 seated below the carpels the condition 

 is described as hypogynous, and the ovary superior. Occasionally in 

 such types the axis may be elongated, so that there is an interval 

 between the series of parts. In the Passion Flower the stamens and 

 carpels are thus carried up a considerable distance above the sepals 



Fig. 1S5. 

 Vertical section of flower of Myos urns, 

 as an example of an li>-pogvnou3 flower. 

 (.\fter Figuier.) 



