June 23, 1905.] 



SCIENCE. 



945 



eies to fungous attacks. It has been stated 

 that the resistance of plants to fungus 

 attacks is due largely to the presence of 

 certain enzymes or toxalbumens present in 

 the cells of the host; and by others it has 

 been suggested that susceptibility is fre- 

 quently a special property due to the pres- 

 ence of certain oxidases, which are regu- 

 lated by external conditions. 



It has been shown that the mosaic dis- 

 ease of tobacco and other similar diseases 

 are accompanied by certain oxidase fer- 

 ments which appear to prevent the diges- 

 tion of reserve food. . The ferment is de- 

 veloped in the growing parts of the plant, 

 it may be transferred from plant to plant, 

 and on the decay of the diseased organism, 

 it is supposed to be set free in the soil. It 

 is believed that it is then capable of dios- 

 mosis and infection of the young seedling. 

 While it can not be shown at present that 

 the enzyme is beyond all question the di- 

 rect cause of the disease, this field of work 

 is certainly one which might yield most 

 interesting results. In this connection it 

 may be stated that peach yellows and sev- 

 eral other important contagious diseases 

 are believed to be of somewhat similar 

 nature. It is also claimed that the keep- 

 ing qualities of fruits may bear a certain 

 relation to the amount of enzymes present 

 at the time of storage ; and, therefore, a 

 knowledge of the time and conditions of 

 the production of such enzymes would have 

 great economic value. 



In general, Czapek found no enzymes to 

 occur in the excretions from the roots of 

 higher plants, and it is now generally be- 

 lieved that the roots of one plant may de- 

 velop no excretions injurious to neighbor- 

 ing plants, and, therefore, there may be no 

 biological relation between the roots of 

 non-parasitic plants associated in the given 

 plant society. It must be said, however, 

 that the information at hand may not be 



taken as final. There are yet some pe- 

 culiar facts with relation to the rotation of 

 crops which may not be readily explained 

 on the groimds of the exhaustion of plant 

 nutrients or of the physical condition of 

 the soil. 



The fermentation of tobacco and tea, or 

 hay and manure, involves enzyme actions 

 which in recent times have received some 

 attention, although the problems which are 

 of most physiological importance require 

 solution. The general belief is that in all 

 cases of enzyme action these compounds do 

 not form a part of the substance upon 

 which their action is exerted, but they act 

 as a key in each particular case, unlocking, 

 or rendering labile, a certain organic com- 

 pound, which is then subject to rearrange- 

 ment and transformation. This is all, 

 however, too speculative for profitable con- 

 sideration, although such speculation may 

 have no evil influence if it is not permitted 

 to encourage the reference of all unusual 

 phenomena to an unusually obscure and 

 difficult process. 



The early perfection of water culture 

 methods permitted a careful study of the 

 mineral nutrient requirements in the high- 

 er plants. Pure culture methods have af- 

 forded a more accurate means of studying 

 the needs of fungi and certain algae. As 

 usually installed, water cultures of the 

 higher plants contain bacteria, so that they 

 afford only a practical test of the require- 

 ments. The problem demands some con- 

 firmatory tests, at least, under pure cul- 

 ture conditions, particularly when organic 

 compounds are employed. It is possible to 

 grow, in a limited way. higher plants under 

 pure culture conditions. 



With the fungi, exact studies may be 

 made upon the influence of the different 

 nutrients on the general form and upon 

 the production of conidia, etc. It has been 

 fcund, for instance, that, in the absence of 



