BOTANICAL SUBJECTS. 325 



XVII.— GEXESIS OF FIBRO-VASCULAK SYSTEM. 



We know tliat the lower plants, from which the higher have 

 evolved, have no such thing as a vascular system. How, then, 

 has this come about ? It surely has not evolved as a ready-made 

 variation. 



The character of vascular tissue is that it is made up of 

 spiral cells. 



Berkeley, in his " Introd. to Crypt. Bot.," p. 72, says : " The 

 total absence of vascular tissue is one of the most general 

 characteristics of Alg^e ; but, as in Phasnogams, the parenchy- 

 matous cells sometimes contain spiral threads, so also there are 

 undoubted instances of spiral threads in Algaa." 



Here we have a statement of a great observer, which leads us 

 to form some conception of how the vascular tissue may have 

 commenced and laid the foundation of what we call vascular 

 plants. 



Berkeley has shown that spiral threads or cells — the elements 

 of the vascular tissue — can be found isolated^ in an erratic state^ 

 in the cellular tissue both of alga3 and pha^nogams. 



Now bacteriologists have discovered spiral microbes^ that isj 

 cells or strings of cells which grow into a spiral. These can 

 infiltrate themselves into the minutest tissue, or, at all events^ 

 their spores can do so. What wonder would it be, then, if the 

 spiral vessels of plants owed their development to spiral microbes^ 

 which gained admission into purely cellular plants as jmrasites, 

 and occupied their intercellular spaces^ thus becoming part and 

 parcel of the cladophyl tissues ? It is conceivable that, in time, 

 this parasite would develop sufficiently, so as to become an 

 important item in the struggle for life of cellular plants. 



Of course such a hypothesis of the genesis of Ihe va>sculiir 

 system would demand that this microscopic parasite should not be 

 harmful to the cellular plant. Quite so. There are numerous 



