CONSTANCY AND MUTABILITY OF FUNGI. 675 



tions in form can only be looked on as stages in the 

 development of the same species, and belong within the 

 boundaries of the species ; further, temporary modifica- 

 tions will arise under the action of definite external 

 influences ; finally, varieties and new species with con- 

 stant hereditary characteristics may be formed from 

 existing species. To what extent the formation of 

 varieties occurs will probably depend on the tendency of 

 the lower fungi to undergo variation ; whether this is 

 great or small can only be decided by direct observations. 

 As in the case of the lower fungi, and more especially in 

 the bacteria, sexual processes are absent, and thus one 

 of the most important factors in the formation of varieties 

 is wanting, we must a priori expect a greater constancy 

 in the species, and a slower variation. On the other 

 hand, the rapid growth and the quick succession of new 

 generations can lead to more rapid occurrence of varia- 

 tions than in the higher plants, and to their formation 

 within measurable periods of time, and, as it were, 

 before our eyes. Nevertheless, it is a question how we 

 should define the individual generations of the fungi. 

 Is every bacteric cell to be regarded as an individual, 

 and does each individual colony represent an innumer- 

 able number of generations, or are the cells of such a 

 colony analogous to those of higher plants, and is it 

 only when fructification and spore formation occurs that 

 a new generation is formed ? 



We thus obtain only a number of open questions, and Results of 

 arrive at the conviction that from the analogy with the Ration bser ~ 

 higher plants we cannot gain any definite conclusions 

 as to the behaviour of the lower fungi ; hence it is only 

 by actual observations and experiments that we can hope 

 for a definite result. 



In so far as observations have gone, we have in the i. Morpho- 

 first place observed all sorts of morphological differences J^e* * dlffer " 

 in the lower fungi. Some of these differences un- 

 doubtedly belong to those which only help to characterise 

 the species. In this sense the processes of growth and 

 development occasion certain alterations in form which 

 are always the same in the same species. We observe 



