I 76 ANATOMY OF THE GYMNOSPERMS 



medium without the development of specialized organs for that 

 purpose. Owing to their minute size they are readily distrib- 

 uted by even slight currents of air, from which they eventually 

 settle as constituents of dust. Their spores offer a remarkable 

 degree of resistance to ordinary conditions, whereby they may 

 survive a most adverse environment for prolonged periods, and 

 again produce the vegetative form when favorable conditions 

 are once more established. It will thus be observed that the 

 growth and operation of such plants is not necessarily continu- 

 ous, but that their action may be intermittent or periodic, as 

 determined by the special circumstances under which they are 

 placed. In any event, the characteristics noted favor, in an 

 exceptionally high degree, the wide prevalence of the effects of 

 which they are the immediate cause. It would be out of place 

 here to enter upon a detailed discussion of these effects, and it 

 will suffice to direct attention to the very general relation of 

 these plants to the production of disease in both plants and 

 animals, while their relation to the disorganization of organic tis- 

 sues is exemplified in the various processes of maceration which 

 constitute so essential a feature in many important industrial 

 processes. 



The second group of plants includes the Fungi, - - plants 

 distinguished by their somewhat higher degree of organization 

 and the development of specialized organs. They are generally 

 multicellular, and the plant body, or mycelium, is in the form of 

 a septate, or nonseptate and branching, microscopic filament, 

 which is capable of very rapid extension, and which may also 

 bring about a vegetative propagation by simple subdivision. At 

 certain stages of its growth, as also under special conditions of 

 moisture and temperature, the mycelium gives rise to asexual 

 reproductive bodies, or spores. Such spores are very minute, 

 and are composed each of a single cell. They may or may not 

 arise through the medium of a sexual process, the fungi exhibit- 

 ing a great diversity in this respect, a discussion of which is 

 unnecessary at this time. The spores are generally produced 

 in vast numbers ; they are most readily distributed by the wind 



