BOTANICAL SUBJECTS. 103 



left stranded there during an ebb. They would germinate in this 

 sort of half-and-half medium, and would live a semi-aquatic life, 

 if suited to the new conditions, or perish if not suited. Some 

 might survive owing to difference of constitution.* Moreover, 

 this transition must have occurred in times when the face of our 

 earth must have been totally different. 



There are many filmy ferns known which cannot exist except in 

 a perpetual spray of water, or in a perpetual surrounding of mist. 



Although we may be incUned to suppose that epiphyte orchids 

 became plants living on trees, owing to a struggle for existence, 

 this may not have been exactly the case. Of course we must 

 suppose that there were trees for orchids to grow upon. The 

 seed of orchids is like fine powder, and can be blown anywhere by 

 the wind. Supposing that some of the seed settled on the fork 

 of a .tree, where there may have been an accumulation of dust 

 and leaf mould, moistened by rain, in a suitable climate, it would 

 germinate and possibly live, and gradually suit itself to such 

 conditions without having been driven to them by a struggle for 

 hfe. 



In the transition of seaweeds to land plants, the survivors would 

 in due course reach places where their roots only, or their roots 

 and lower leaves, would be submerged, and their higher parts be 

 in an air medium. Ranunculus aquatilis, for instance, and 

 several other plants, may be survivals of this transition state. 

 They have leaves which are suited to a submerged life, and others 

 suited to an air life. Even before insects, birds, and other animals 

 came into existence, the tides would appear to have been sufficient 

 to help the evolution, first of semi-aquatic, and then of wholly 

 land plants. Subsequently the wind would carry their spores and 

 seeds further inland and up mountains. 



In this transition from water, through palustral, moist, and 

 finally to dry land ; from low alluvial soil to rocky highlands and 

 deserts, in addition to needing water, with mineral ingredients in 

 it, as of old, plants would have had to gradually adapt themselves 

 to a multitude of new surroundings. 



As plants passed from a water to an air life, a circulation of 

 fluids would have become a sine qua non, because the roots would 



* We continually see a difference of constitution in the seeds of the same 

 pod, and in the young of the same litter. 



