58 PLANT-LIFE ON LAND [OH. 



It is by no means outside the bounds of possibility 

 that this theory of sterilisation may be near to the 

 ultimate truth. But at present we are not in a 

 position to look with any certainty so far back as to 

 the ultimate origin of either the vegetative or the 

 propagative system of the spore-bearing plant. A 

 third view which does not raise questions of ultimate 

 origin has, however, been suggested by a comparison 

 of the simpler Vascular plants. It appears to stand 

 upon a sound basis of fact and of logical reasoning, 

 for it starts not from any hypothetical forms, but 

 from such plants as we can see living to day. It is 

 that the whole shoot of relatively primitive Vascular 

 plants was non-specialised : it served as a general- 

 purposes shoot. Both functions had to be performed 

 by it in earlier times. But in the course of evolution 

 of higher types differentiation took place, so that a 

 certain region became specially developed to carry 

 on nutrition, another region of the shoot produced 

 spores. The result of this is that the two functions 

 are carried out by distinct regions of the shoot 

 specially developed for the purpose. The vegetative 

 region habitually comes first in the individual life, 

 the propagative region, or " flower " as it is called in 

 the higher plants, appears only late after the plant 

 has acquired sufficient material for the formation 

 of the propagative organs. It is by comparison 

 of Seed-plants with the lower Vascular plants that 



