33'2 Causes axd Course of Ohganic Evolution 



living host, or later to two alternating hosts; by formation 

 of several kinds of asexual gonidial cells and of sex-cells; by 

 exposure at one season of the year to one set or intensity of 

 environal agents, and at another season to a different set; by 

 variations in the host-})lants, or in the organic nutritive medium, 

 and reflex variation in the fungus; that remarkable wealth 

 of species has evolved, to slight degree in fresh water, to a 

 ^'ery small degree in salt water, and in exceptional degree 

 on land, that are now omnipresent and preponderatingly rich 

 in individuals. 



So, from all the experimental and observational evidence to 

 hand regarding the bacteria and fungi, we would conclude 

 that these show abimdant hereditary characters, but that 

 they also show variation-effect owing to action and reaction 

 between them and their environal surroundings; that, in con- 

 stantly responding to the sum-total of most satisfying environal 

 agents, they have projected proenvironal variations that have 

 given rise to new species; and that during the process other 

 types of the fungi, that were imperfectly suited to their envir- 

 onment, have died out. The last result would frequently 

 occur when some species of plant or animal that acted as a 

 host, and on which some fungoid species was holoparasitic, 

 died out. But it is as true that, when plant and animal species 

 increased and occupied every suitable area, the production 

 of new bacterial and fungoid species would also be possible. 

 This it is which explains the enormous number of species now 

 alive, as compared with the algae, from which the fungi ^^'ere 

 primitively derived according to the above accepted views. 



The exact chemico-physical and biological correlation that 

 exists between most bacteria and fungi on the one hand, and 

 their hosts on the other, is well shown in the nitrifying, the 

 ginger-beer, and the leprous bacteria, also in the potato fungus, 

 the black knot fungus, and the oak Dcedalea (DcBclalea quercina) 

 amongst many others. 



But, before passing from the fungi, special attention should 

 be given to the fact that, in spite of their ancient origin — as 

 rare pala'ontological evidence sufficiently testifies — they have 



