280 Univcrsitjf of California Puhlicat'iouA in Agricultural Sciences [Vol. 1 



development and the unfavorable treatments, or the untreated 

 soils, of short, thick roots having very few fibrous roots. The 

 two exceptionally large root yields in pot 4 and pot 15 are not 

 capable of satisfactory explanation at this time. 



It is not our purpose to explain at this time in detail the 

 causes underlying the positive or negative effects of the various 

 treatments, since such explanations will appear in the more com- 

 plete reports of the work which are to follow. It may be said 

 here briefly, however, that the H.SO^ exerted its influence, both 

 in the direction of neutralizing the NaoCO.. and that of improv- 

 ing the soil's physical condition through its shrinkage of colloids. 

 In smaller measure, likewise, gypsum exerted similar effects and 

 in addition thereto exerted the characteristically strong antag- 

 onistic effect to the sodium and acid ions which calcium is known 

 to exert in the plant world. The effects of FeS04 are to be 

 explained in general as are those of CaS04. The effect of the 

 barnyard manure is probably exerted through the organic colloids 

 produced in its decomposition, which through the enormous sur- 

 face they possess hold much of the salts or components of the 

 latter in a condition which prevents their ready solution in the 

 soil water. Moreover, the organic colloids render the soil more 

 retentive of moisture, therefore diluting the soil solution, and 

 besides exert the most marked effects of any of the materials 

 used in the improvement of physical conditions in the soil. ]\lany 

 other effects are probably also involved in the manure treatment 

 which, like those above mentioned, cannot be discussed here. 



Detailed studies are now being made of a chemical, physical 

 and biological nature to determine, so far as may be. the intimate 

 effects concerned in treatments of the soil which are above out- 

 lined. ]\Iuch material has already been accumulated from these 

 supplementary studies which is of great practical as well as 

 theoretical significance. 



No less interesting and striking than the data given in Table 1 

 is the series of photographs accompanying this paper. These 

 confirm in the appearance of the plant growth what is so clearly 

 shown in the record of yields as above discussed, and the reader's 

 attention is particularly directed to them. 



