INTRODUCTION 9 



and one stage of the cycle can repeat itself. Dietel has 

 proved experimentally that the aecidium condition of 

 certain species of Puccinia and Uromyccs can be repeated 

 by aecidiospores when sown on a similar host to that on 

 which they were produced, without the intervention of 

 the uredospore or teleutospore stages. 



The researches of Klebs are especially significant in 

 connection with * pure cultures,' which by some are placed 

 on a par with Caesar's wife. In future, instead of arguing 

 that such cultures prove incontestably the normal sequence 

 of development of a species, we should only go so far as 

 to say that those show what the particular fungus could do 

 under a special sequence of conditions. 



The nutrient medium commenced with is constantly 

 changing in composition, density, humidity, etc. ; in fact 

 it passes through that sequence of changes which Klebs 

 has indicated necessary to effect radical changes in the 

 behaviour of the fungus under experiment. 



As previously stated, cytology has not as yet furnished 

 evidence sufficient for the formulation of a new and 

 improved scheme of classification. New schemes, how- 

 ever, are not lacking. Meyer, on the strength of agree- 

 ment in possessing ' continuity of protoplasm,' and 

 fusions in vegetative cells, derives all fungi from the 

 Florideae. The Uredineae break away first and recede 

 in a straight line, giving off at an angle the Ustilagineae. 

 These are quickly followed by the Basidiomycetes ; the 

 Ascomycetes being the last to start on an independent 

 fungal existence. Why other groups of plants showing 

 continuity of protoplasm even more clearly than fungi are 

 not included in this idea of evolution, is not stated. 



Juel has propounded a classification of the Basidiomy- 



