iSo ANATOMY OF THE GYMNOSPERMS 



directly from the air, or indirectly through the medium of the 

 surrounding fluid, such as water, in which the organism may be 

 growing. Such ae robes cannot exist when the supply of oxy- 

 gen from either of the sources indicated is cut off, since their 

 respiratory function is inhibited and all dependent activities 

 necessarily cease. It is true that some plants, such as certain of 

 the bacteria, cannot live under such conditions of free aeration, in- 

 asmuch as they have become adapted to obtaining their oxygen 

 from the products of organic decomposition, and any access of 

 air or free oxygen at once inhibits their growth. Such anaerobes 

 form a comparatively small but none the less exceedingly im- 

 portant group of plants, and it is a knowledge of these differences 

 in the life history of the organism which enables us to gain an 

 intelligent insight into the operation of the various forms of 

 organic decay. It may be stated, then, that the fungi in general 

 cannot grow except under conditions which afford a free supply 

 of oxygen, and this fact supplies the basic principle on which to 

 found methods for retarding or permanently arresting the oper- 

 ation of fungi. But it will be found in practice that this is 

 further dependent upon the remaining factors of warmth and 

 moisture. In the preceding chapter it has been shown that the 

 spores of fungi, as also those of the bacteria, are capable of enter- 

 ing upon a resting state whereby they become capable of resist- 

 ing very adverse influences, but that they are also capable of 

 once more germinating, sometimes after the lapse of several 

 years, when again brought under favorable conditions. These 

 conditions are (i) a suitable temperature, and (2) an abundance 

 of moisture. The consideration of a few special cases will per- 

 mit of a clearer conception of the nature and operation of these 

 conditions. 



That all fungi arc not equally affected by the same degree of 

 heat and cold is one of the elementary facts of plant physiology, 

 while it is also equally well known that the same plant will be 

 variously affected according to the special condition of growth 

 in which it is brought under the action of varying temperatures. 

 These facts are probably illustrated among the bacteria in a 



