PAKT L 

 MORPHOLOGY, 



Introductory. The province of morphology is the study of 

 the form of the body of plants, including the development of the 

 body, the segmentation of the body into members, and the form 

 and mutual relations of the members, as also the intimate struc- 

 ture (Anatomy and Histology) of the body and its members in 

 so far as structure throws light upon the morphology of any part 

 of the body. It is an essentially comparative study : it classifies 

 into categories the members of a plant, or those of various plants, 

 according to their morphological nature, that is, according to the 

 mode and relations of their development. Each category consists 

 of homologous members ; of members, that is, which essentially 

 agree in the mode and relations of their development ; or, in 

 other words, which are more or less nearly equivalent morphologi- 

 cally, because they are of common descent. 



There are various degrees of Homology, that is, of morphological relationship. 

 General homology exists between homologous members when the one is not 

 the precise equivalent of the other ; for instance, the sporogonium of a Moss 

 is generally homologous with a Fern-plant ; and again, the sporangium of Lyco- 

 podium, being borne singly on a sporophyll, is generally homologous with all 

 the sporangia, collectively, borne on a sporophyll of an Osmuuda. Special 

 homology exists between two homologous members when the one is the precise 

 equivalent of the other. When this is true in detail, the special homology is 

 said to be complete : for instance, the foliage-leaves, the perianth-leaves, and the 

 sporophylls of a Phanerogam are all specially homologous, they all belong to 

 the one category, leaves ; but complete special homology can only exist between 

 the members of each sub-division of the category, between foliage-leaf and 

 foliage-leaf, perianth-leaf and perianth-leaf, and so on. The special homology 

 is incomplete when the members compared present differences in detail ; thus 

 between foliage-leaves, perianth-leaves, and sporophylls there exists incomplete 

 special homology ; or again, the sporangia of eusporangiate plants are incom- 

 pletely homologous with those of leptosporangiate plants. Members may have 

 both their general and their special homologies ; thus whilst the sporangium 

 of a Lycopodium is generally homologous with all the sporangia on the 

 sporophyll of an Osmunda, it is specially homologous with each individual 

 sporangium. Homologous members are termed the homologues of eacb other. 



Morphology does not, however, include the consideration of the 



V. S. B. B 



