THIRTY-FOURTPI FRUIT-GROOVERS ' CONO^NTION. 



81 



factors, their general intluenee upon plant life is well known. ^Ye are 

 all aware, for instance, that water is indispensable, but that either 

 too much or too little is injurious. Also that the same is true in 

 regard to sunlight, heat, cold, and chemical food elements. AYhile an 

 excess of any of these factors may produce a very evident injurious 

 effect on the plant, scarcely dift'erent from a mechanical injury, yet, 

 when relative conditions in regard to these essential factors become 

 complicated, we may and often do get results upon plants which are 

 strictly of the nature of disease with definite symptoms, in which it is 

 very difficult to establish definitely a simple succession of cause and 

 effect. 



We mi\st further consider the fact brought out at the beginning of 

 this paper, that simply a condition of natural health is not sufficient 

 to satisfy commercial reciuirements, but that certain definite standards 

 are set up of ciuality and quantity of the product, some of which may 

 be radically different from those which Nature, so to speak, intended. 

 From this standpoint, the control of the effect of natural conditions 

 upon cultivated plants may be of even greater importance in relation 

 to these more or less artificial qualities than as simply aff'ecting ordinary 

 health. Horticultural conditions in California are of such a nature 

 as to make this phase of the subject of particular importance. Our 

 crops are grown largely imder conditions which are entirely artificial, 

 the plants themselves being natives of other portions of the world, 

 and grown here in places where the conditions which Nature .ordinarily 

 supplies are largely under the control of man. Two factors particu- 

 larly, those of irrigation and fertilization, are of the greatest impor- 

 tances in this connection. In the citrus industry we plant a tree in a 

 place where it would perish almost immediately without constant 

 attention, and have at our disposal to withhold or supply, in any desired 

 amount, two of the most important factors in plant growth, water and 

 soil food. The amount to be supplied, the time of application, 

 frequency, and many other most important considerations are very 

 largely in the hands of the grower, and the growth of the tree, its 

 health, life, and development, as well as the quality and quantity of 

 its fruit, depend almost entirely upon the manner in which the grower 

 handles these controllable factors. 



It is further to be said that there is no tree more sensitive or easily 

 affected by conditions of this sort than the orange or lemon. 



To come more directly to the subject which we are expected to discuss, 

 we may say, in general, that in our investigations of the diseases of 

 citrus trees in California we have found almo.st nothing which may 

 be ascribed to the effects of any parasite : that is to say, we know of 

 no important citrus disease which is caused by any fungus or bacterial 

 organism, or anything of that nature. If we except decay of the fruit 

 and a very few exceptional cases of disease of the tree, the above state- 

 ment may be made an absolute one. It is true beyond all question that 

 our most serious troubles with citrus trees in California are the effects 

 upon the tree of unfavorable natural conditions, and not those of active 

 parasites. Some of these effects, it must be confessed, are at present 

 most obscure and difficult or impossible to account for in any satis- 

 factory manner. Yet the study of the various diseases, and of the 

 nature of the tree itself, has been sufficient to show that this is true. 



6 ^FGC 



