CH. x] GENERAL OUTLOOK 155 



Further, among Fungi some forms appear to omit 

 entirely certain stages which are shown in allied 

 forms. The life-history may thus be curtailed and 

 simplified. It is only with some limitation therefore 

 that the thesis is to be accepted that the simpler 

 organisms give a key to the problem of Descent. 

 Subject to such necessary limitations, the comparative 

 method may be adopted, and we may state a current 

 theory of the Origin of the Vegetation of the Earth 

 based upon such comparisons. As we do so we 

 may recognise how readily it accords with the 

 limited facts advanced in the foregoing pages. 



A great body of evidence indicates that the 

 origin of Plant-Life on Land was from aquatic 

 surroundings. The water-problem is at the base 

 of the whole physiology of Land plants. There 

 is no requirement so imperative, and no adaptation 

 so exact, as that for the supply and the control of 

 the water which forms so large a constituent of 

 any Plant of the Land. The stability of the plant 

 while young, as well as the functional activity of 

 each cell of its body during life, depend upon a 

 balance of gain and loss of water being duly 

 maintained. The relative ease of aquatic plants as 

 regards their water-supply, compared with the almost 

 desperate shifts of many terrestrial plants, suggests 

 with some cogency that the latter is the derivative 

 and specialised, the former the primitive habitat. 



