170 MORPHOLOGICAL DEVELOPMENT. 



Agrimony is so small, that unless visited by insects of a 

 corresponding size which settle as bees and butterflies settle, 

 its parts will not be affected in the alleged manner. That 

 all anomalies of this kind can at once be satisfactorily ex- 

 plained, is scarcely to be expected : the circumstances of each 

 case have to be studied. But it seems not improbable that 

 they are due to causes of the kind indicated.* 



§ 235. We have already glanced at clusters of flowers for 

 the purpose of considering their shapes as clusters. We must 

 now return to them to observe the modifications undergone 

 by their component flowers. Among these occur illustrations 

 of great significance. 



An example of transition from the radial to the bilateral 

 form in clustered flowers of the same species, is furnished by 

 the cultivated Geraniums, called by florists Pelargoniums. 

 Some of these, bearing somewhat small terminal clusters of 

 flowers, which are closely packed together with their faces 

 almost upwards, have radially-symmetrical flowers. But 

 among other varieties having terminal clusters of which the 

 members are mutually thrust on one side by crowding, the 

 flowers depart very considerably from the radial shape 



* It is objected to the above interpretation that " many flowers of sizes 

 intermediate between the Hollyhock and the Agrimony are radially sym- 

 metrical and yet grow sideways. I may mention various Ziliacece, e.g. Chlo- 

 rophytum, Eitcomis, Muscari, Anthericvm. Sagittaria, also, has many of its 

 flowers in this position. Further, if the higher insects alight on flowers in 

 a definite way. as they do, the parts of the flower must bear different rela- 

 tions to the visiting insect, however large, so that flowers unvisited ought 

 all to be zygomorphic." My reply is that in the sense which here concerns 

 us, the different petals of the Hollyhock -flower do not bear different rela- 

 tions to the visiting insect ; since, practically, the upper and lateral petals 

 bear no physical relations at all : in so far as the visiting bee is concerned 

 they are non-existent. The argument implies that change in the form of a 

 flower from the radial to the bilateral is likely to take place only when the 

 contact-relations of the petals to the visiting insect, are such as to make some 

 forms facilitate its action more than others ; and the large petals of the 

 Hollyhock cannot facilitate its action at all. In respect of the LiHacece 

 instanced, it is needful to inquire whether the structures are such that this 

 alleged cause of bilateral symmetry can come into play. 



