THE INFLORESCENCE, AND THE FLOWER 275 



of final analysis, be regarded as a simple shoot bearing sporangia, 

 modified in the course of its evolution along lines of specialisation 

 such as those specified above. Structurally its shoot-nature is evident 

 in the less specialised examples, though in the more highly specialised 

 it may be so hidden by peculiarities of form as to be recognisable 

 only after careful analysis and comparison. Moreover, those several 

 factors of specialisation, which have been discussed and illustrated 

 in the preceding pages, may take effect in the most varied combination, 

 so that the analysis which is required to reduce a complicated flower 

 to terms of construction comparable to that of an ordinary leafy 

 shoot may demand both skill and insight. But this is greatly aided 

 if the student can realise, in the first place, the probable evolutionary 

 steps by which the peculiar structure was produced : and secondly, 

 the biological advantage which follows from it. The most obvious 

 end served by the mechanism of the flower is the transfer of pollen 

 from the stamen to the carpel. This is a necessary step, though by 

 no means the only important one, in normal reproduction. For 

 carrying this out Seed-Plants are dependent upon external agencies, 

 such as wind, water, or animal activity. Since Plants are fixed in 

 the soil and immobile, such agencies must be resorted to if the advan- 

 tage of intercrossing is to be secured. It is such considerations as 

 these which make the variety and intricacy of the forms which flowers 

 show biologically intelligible, and give a special interest to the study 

 of their evolutionary origin. 



It is possible by comparison to follow the general trend of evolu- 

 tionary advance from floral types which may be held to be relatively 

 primitive to those which are advanced and specialised. The former 

 are more like the normal vegetative shoots in the arrangement and 

 mutual relations of their parts : the latter diverge in more or less 

 marked degree from that simple state. It is generally accepted 

 that a primitive type of Angiospermic flower was hermaphrodite, and 

 that its numerous parts were inserted separately, and in acropetal 

 order upon an elongated receptacle ; and that they were arranged 

 after a spiral plan. This type of construction is seen in the Mag- 

 noliaceae, and other related types, such as the Buttercups and Water- 

 lilies. On the other hand it seems probable that very simple unisexual 

 flowers also existed in early times, such as are seen in the Willows. 

 It is significant that both the Magnoliaceae and the Salicaceae occur 

 early as fossils, and are in fact recorded from low horizons of the 

 Cretaceous Period. It is, however, in the hermaphrodite types that 

 the lines of floral specialisation can be most readily traced. 



