BOTANICAL SUBJECTS. 39 



We can see how easy it would be for all the crowded florets 

 of a composite head to become suppressed, except one of the ray, 

 and that to become the irregular corolla of the LabiatcB^ 

 Lobelia, and others ; or for all the florets of the disk to become 

 suppressed, excepting one, and that to become the regular flower 

 of a Bouvardia and others. "We are accustomed to look upon the 

 compositfe as something different from other flowering plants, but 

 scatter the head of composite florets, by giving each a lengthened 

 peduncle, and you have the loose head of flowers or branch of a 

 Russellia, and others, dispersed on an expanded and highly- 

 branched stem. 



As a matter of fact, we already have the composite head 

 scattered to some extent in Centra/itkus, Valeriana, Ixora, 

 Viburnum, and many others. 



Curiously enough, in one of the Rutaceae — Diplolcena Dampieri 

 — we have the scattered flowers gathered up into a composite head ! 



It is impossible to behold a tropical forest, or the vegetation of 

 a desert or of some high altitude, and not feel convinced that 

 surroundings influence variation. If surroundings have no 

 influence on variation, why has Ficus repens, when grown- 

 against a wall, one form of leaf, and when grown as a standard, 

 a different form ? * The same might be said of other walJ- 

 climbing plants. 



There is a tendency now to attribute all variation to congenital 

 changes, initiated by sexual conjugation, that is the union of a 

 male and female cell. 



What is a congenital variation ? It is (a.) a variation which 

 appears at birth, as a further development of some atomic changes, 

 which occur during the progress of foetal growth ;"{■ or (h.) a 

 variation, which appears in after life, owing to some similar atomic 

 change having occurred also during foetal Ufe, but which does not 

 become apparent at birth, and, may be, not for many years after 

 birth. 



Now, is it true that sexual conjugation is the only cause of 

 congenital variation, and that surroundings have no influence 

 whatever in producing it ? 



* See Gardeners^ Chronicle, 10 January 1891. 



t Under the name of " foetal growth " may be here included the growth 

 of seeds in their parental ovary. 



