F HISTORY AND SCOPE OF PLANT PATHOLOGY 163 



dreaded among cultivators. There are some abstruse and what 

 to many are theoretical questions which need to receive careful 

 answers in order to supply proper guidance for those working upon 

 avowedly practical problems. 



But I am in danger of infringing upon the ground of the speaker 

 who is to follow me. It does not, in fact, come into the province 

 of this discourse to speak of work under way at this time, or to 

 point out the unsolved problems, except to indicate the branches 

 of knowledge whose methods or facts are being turned to account. 



I may at this point barely touch upon the aid that cytology is 

 rendering to pathology by the illumination which it brings into the 

 matter of the intricate life-histories of many parasitic fungi. Just 

 at present we are awaiting with much interest the cytological results 

 of investigations into the nuclear history of rust-fungi, in order to 

 determine which sets of spores have merely conidial or vegetative 

 powers, and which have sexual and consequently more intense 

 powers of reproduction. Such knowledge will enable us to direct 

 our attacks upon their activity with greater clearness and accur- 

 acy. 



Taking a general survey of the field, the advance since 1880 is 

 most largely along the study of parasitic diseases, and especially 

 of the organisms which produce these diseases. It is natural that 

 the life-histories of the fungi should first receive attention, especially 

 the numerous small forms on field crops, and that the work should 

 extend gradually to the large but frequently obscure forms on forest 

 trees, and then to the minute and more obscure micro-organisms, 

 the bacteria, yeasts, and possibly amoeboid forms. Up to the present 

 time the energy of investigators has been largety absorbed in study- 

 ing the inciters of disease; the means by which the assaulting 

 organism overcomes the resistance of the host has received small 

 elucidation, and the nature of the physiological perturbations in- 

 duced by the parasitic organisms, or by any other cause, is almost 

 an unexplored field. 



If I have said little about bacterial diseases, which have been 

 studied with such brilliant success and with such clear and discrim- 

 inating judgment by Erwin F. Smith of Washington, or of diseases 

 caused by enzymes, to which we were introduced by the researches 

 of Loew, or of the well-marked diseases of unknown origin, such as 

 yellows and rosette of peach-trees, it is that I do not doubt but you 

 will hear them more ably and entertainingly presented by my suc- 

 cessor upon the programme. Neither is it desirable that I should 

 discuss the advance likely to be brought about by the new theories 

 and methods in the study of the action of poisons, as these are 

 applied to the explanation of diseases, as well as to the devising of 

 remedies. 



