BOTANY OF THE LIVING PLANT 



, ,1 belief that the flower had resulted from changes wrought in some 



p, tat shoot. 



we direct our attention solely to the Flowering Plants this opinion 

 might stand. But as the nineteenth century drew on, knowledge of the lower 

 forms greatly increased, especially in the case of such plants as the Ferns and 

 Club-Mosses. This has supplied the material necessary for a revised theory of 

 the origin of the flower. Checked by these comparisons we may now figure, on 

 a basis of fact, rather than of semi-poetical surmise, how the flower as distinct 

 Erom the vegetative region originated in the higher plants. The main point 

 to bear in mind is that the propagative function must have recurred in each 

 fully completed life-cycle throughout descent. Hence the production of 

 sporangia was never an innovation, and they cannot at any time in the course 

 of descent have been imposed upon a pre-existent vegetative system, as 

 Goethe's theory would assume. The facts suggest that the whole shoot of 

 relatively primitive Vascular Plants was non-specialised. It served general 

 purposes, both for vegetation and propagation. But in the course of evolution of 

 higher types differentiation took place, so that a certain region became exclusively 

 vegetative, while another produced sporangia. Thus a theory of Segregation 

 takes the place of a theory of Metamorphosis. The vegetative phase naturally 

 comes first in the individual life, so as to supply the necessary materials for 

 propagation. Once these two pristine functions were allocated to distinct 

 regions of the plant, each was open to its own distinct specialisation. And so 

 it comes about that while in simple cases there may be some similarity 

 between the flower and the foliage shoot, the two may diverge widely in more 

 advanced types. But, however greatly they may differ, the flower and the 

 foliage shoot are to be held as the results of segregation of parts of an 

 originally general-purposes shoot. This gives a natural meaning to those 

 structural resemblances, which are sometimes so striking, between the foliage 

 shoot and the flower which it ultimately bears. 



In such discussions as this the antithesis between the flower and the foliage 

 shoot is apt to be drawn more strongly than the facts warrant. The flower 

 is not always clearly defined from the vegetative region. Comparison of the 

 flowers of Cactaceae and Magnoliaceae, and of some Grasses such as 

 Streptochaete, show that bracts may merge gradually into floral organs. A 

 further comparison with Conifers, Cycads, and Club-Mosses will confirm the 

 view that the two regions have not always been as distinct as they now appear 

 to be in the Higher Flowering Plants. 



In the earlier part of this Chapter the more important lines have 

 been sketched along which the analysis of floral construction may 

 be undertaken. Such analysis is a necessary basis for comparison, 

 and ultimately for classification. But this will not be pursued further 

 al present. It is also necessary as a step towards realising how the 

 mechanism of the flower works. An engineer cannot properly under- 



ind his engine till he has taken it down. But the engine will not 

 work till the parts are again assembled. Similarly the student must 

 not be content with the mere analysis of the flower. After analysis 



