ORGANIC FORM AND ARCHITECTURE 679 



ascidians, etc., was becoming clear, the attractive speculation that 

 the branching growth of plants might be similarly interpreted was 

 ventured by Gaudichaud, who argued that each leaf, with its 

 appropriate portion of stem, should be considered as the essential 

 unit, which he called the "phyton"; and which, by its budding of 

 new ones, develops the vegetative system, from which again, as a 

 crowded and integrated grouping of phytons, appeared the flower. 

 The familiar view of the stem developing its own leaves, however, 

 prevailed; with the fascinating homologies of bud and shoot, so 

 intelligibly condensed to bulb, or differentiated to flower. 



Yet now we have in recent years the strenuous, elaborate and 

 undeniably skilful developmental and histological labours of M. 

 Chauveau, who so far returns to Gaudichaud's theory, yet with 

 modification ; and this with a refinement of investigation and vigour 

 of argument which compel respect. Though most botanists remain 

 as yet unconvinced, it is not easy for them or us to disprove his 

 critical explanations of their conservatism. His unit, and thus 

 miniature plant, he calls the phyllorhiza, essentially a leaf with 

 rootlet. Repeated budding and coalescence give rise to the stem, 

 which is thus no longer viewed as primary, but as a secondary 

 formation. But all that we are concerned with here is to illustrate 

 morphological enquiry. 



ANALOGY. — ^When organs have a functional resemblance, dis- 

 charging the same chief role, they are said to be analogous, whether 

 they are homologous or not. Thus lungs and gills are analogous, 

 both being organs of respiration, but they are not in any sense 

 homologous; thus a Vertebrate's lung is a hollow outgrowth from 

 the anterior part of the food-canal and the gills of a typical fish are 

 feathery structures growing out from the sides of gill-clefts, which 

 again are outgrowths from the pharynx. There may be some deep 

 similarity between a lung and a gill-cleft, since both are outgrowths 

 from the alimentary canal, but there is no possibility of homo- 

 logising a hollow bag with a group of feathery filaments. 



The first clear focusing of the contrast between homology 

 (developmental and structural resemblance) and analogy (functional 

 resemblance) is due to Sir Richard Owen. Three of his illustrations 

 may be given : 



{a) the wing of a bird and the arm of man are homologous, but 



not analogous; 

 {b) the wing of a bird and the wing of a butterfly are analogous 



but not homologous; both are organs of true flight, but 



they are entirely different in structure and development ; 

 (c) the wing of a bird and the wing of a bat are at once analogous 



and homologous, for both are organs of true flight, and both 



