GENERAL REVIEW OF CRYPTOGAMS. 149 



easily, while others retain their vitality so tenaciously as 

 to make it almost impossible to destroy them. Spores of 

 some of the bacteria, for example, endure great extremes 

 of temperature, and may be subjected to a great variety of 

 vicissitudes without suffering any injury. The process of 

 sterilizing, which plays so important a part in pathology, 

 in biological investigations, and even in commercial manu- 

 factures, i^ based on the exposure of whatever it is desired 

 to sterilize to a temperature that disease germs cannot 

 withstand. In treating grains for the destruction of smuts 

 before sowing, it becomes a delicate operation to ascertain 

 and employ a degree of heat that will kill the spores and 

 leave the grain uninjured. This, however, has been suc- 

 cessfully accomplished, and is one 6f the practical opera- 

 tions well known to intelligent farmers. 



Passing from germination to the vegetative growth that 

 follows, we find that each class of cryptogams has its own 

 characteristic features, sufficiently marked to be vegetative 

 stated in general terms, and to serve for the organs, 

 recognition of the class. The vegetative body of a fungus 

 is a mycelium. It consists, as we have seen, of a collec- 

 tion of hyphse, loosely or closely aggregated, or compacted 

 into a hardened or fleshy mass ; but, however modified, an 

 examination of its anatomical structure reveals its true 

 nature. It is this, rather than any theoretical considera- 

 tion, that has defined the actual position of lichens, and 

 requires their classification with fungi; and again, the 

 fungous nature of rhizomorphs (root-like bodies growing 

 in decaying wood) is at once recognized by the same 

 structural test. The vegetative body of the algse is some- 

 thing widely different. It may consist of a single cell, as 

 in the case of Vaucheria, but more commonly it is com- 

 posed of numerous cells, forming a filament as in Spirogyra, 



