52 PLANT-LIFE ON LAND [CH. 



shoots terminate in a compact aggregate of leaves, 

 which is called a bud : and so, at least in the young 

 state, the vegetative shoot may resemble the flower 

 so far as the aggregation of its parts is concerned. 



It thus appears that there are marked analogies 

 between the foliage-shoot and the flower. This leads 

 to the question whether there is any absolute diflference 

 between them. It will lie near to the hand to suggest 

 the qualities of texture of the parts, of their colour, 

 or their scent, by which flowers are apt to be charac- 

 terised as distinct from vegetative shoots. But 

 none of these are constant features in the one or 

 entirely absent from the other. There is, however, 

 one absolutely distinctive character. It is the 

 presence in the flower of the organs of propagation 

 called "sporangia." These are of two sorts, on the 

 one hand the ovules which mature into the seeds, on 

 the other the pollen-sacs which produce the pollen. 

 It is the presence of either or both of these which 

 stamps the flower as distinct from a foliage-shoot 

 (Fig. 10). 



However different these two essential organs of 

 the flower, the ovule and the pollen-sac, may seem to 

 be to day, there is good reason for holding them to 

 be modifications produced in descent from a single 

 primitive type of sporangium. This organ had as 

 its office the production of spores or separate germs 

 shed from the parent. In the more primitive plants 



