1 8 Robinson, Puccinia malvacearuin and its host plant. 



round the nucleus and ultimately disintegrate, and that 

 the chromatin diminishes in amount, shows,' that, though 

 these cells are still living and plasmolysable, their vital 

 activities are diminishing, and they are dying in a pro- 

 tracted fashion. 



Magnus^* records that in the case of Pucciiiia leuco- 

 spei'nia, the haustoria arise relatively late in the attack, 

 and therefore concludes that the main nourishment of the 

 fungus is accomplished by the osmotic activity of the 

 intercellular mycelium. In the present case, the fungus 

 establishes connection with the cells of the host by means 

 of haustoria immediately after infection. It is therefore 

 likely that these haustoria obtain, from the living cells, 

 materials which are essential to the development of the 

 fungus. 



The question of the relations of a parasitic fungus 

 and the tissues of its host is a very complex one, and its 

 exact analysis or even description is difficult. While 

 some of the observations recorded in this paper are 

 simply confirmatory of those recorded by other investi- 

 gators, it is hoped that some advance has been made ; 

 especially as regards the exact relations of the haustoria 

 to the cytoplasm and the nucleus of the cells attacked 

 and the vitality of these cells. In studying this question, 

 the simple process of examining uninjured living cells has 

 proved of great assistance and an invaluable check on the 

 appearances shown in permanent preparations. Another 

 aspect of the disease caused by this fungus has been at 

 least indicated by the study of the starch-distribu lionin 

 the affected regions. In conclusion, I desire to express 

 my indebtedness to Professor W. H. Lang for suggesting 

 this work and for his continual advice and assistance 

 during its progress. I have also had the advantage of 



1** Loc. cit., p. 213. 



