PARTIAL DICLINISM. 227 



Androdicecism and Andromoncecism.* — These conditions 

 do not appear to prevail to the same extent as the female 

 forms of flowers. Both of these kinds are not at all un- 

 common in the Umhelliferce, and are a result of exhaustion, 

 for the umbels produced at the end of the season are often 

 entirely male ; or, if at other periods, it is generally the 

 central florets which develop no pistils, as in Astrantia minor. 

 Miiller has noticed how " the weaker plants usually bear but 

 one umbel consisting only of male flowers." This would 

 make it androdioecious. I find that andromoncecism prevails 

 in Astrantia major, Gariim, Smyrnium, and in Trinia vulgaris. 

 This last, growing on the Clifton downs, bore umbels which 

 were altogether male, after the hermaphrodite ones had 

 formed their fruit. Daucus grandiflora is remarkable for 

 having three kinds of flowers. According to Miiller, the 

 central ones are male; at the edge of the umbellule the 

 flowers are neuter, with the outermost petal greatly enlarged; 

 lastly, at the margin of the whole umbel, are female florets 

 in which the outer petals attain to a gigantic size.f 



* Androdioecism signifies that the same species has both male and 

 hermaphrodite plants. 



Andromoncecism signifies that the same plant bears both male and 

 hermaphrodite flowers. 



t I would here remind the reader that the interpretation given 

 above (Chapters XI.-XIII.) of the origin of irregular corollas, applies 

 equally well to those cases where it is only in the outermost florets of a 

 cluster where the petals are enlarged, as in Iberis, many of the Com- 

 positoe, and UmhellifercB, as well as in Hydrangea, Guelder Rose, etc. In 

 all these, when insects first approach the umbel and alight on the border 

 of it, any or each individual floret on the margin may have to carry the 

 burden. As soon, however, as the insect passes the edge of the cluster, 

 its weight is distributed over several florets ; so that they are not sub- 

 mitted to any special strains upon one, i.e. the outer side only. The 

 same remarks apply to Mentha, as compared with Lamium. The insect 

 visits one flower at a time in the latter, but scrambles over several in 

 the former, which has (presumably) degraded in consequence. 



