January 14, 1898.] 



SCIENCE. 



47 



free acid or acid humates already formed, 

 and no humus in the absence of oxygen 

 can be converted into an acid and thus in- 

 crease the amount of carbon dioxid evolved. 

 The quantity of carbon dioxid evolved is 

 estimated by the usual methods and thus 

 an exact measure of the total acidity is se- 

 cured. (Chemiker-Zeitung, March, 1897, 

 p. 174.) 



The claim has been repeatedly made that 

 soda can replace potash to a certain extent 

 in plant growth. The physical and chem- 

 ical similarity between these two substances 

 is so great that it would not be surprising 

 to find also a physiological I'esemblance. 

 Wagner, in fact, claims to have demon- 

 strated that a slightly less quantity of 

 potash is needed for plant growth, pro- 

 vided abundant supplies of sodium are 

 present. These deductions of Wagner, 

 however, have not been confirmed by other 

 experimenters. When good effects have 

 followed the application of soda it has 

 been demonstrated that it is due to other 

 causes than the replacement of potash 

 in plant tissues. Soda in certain circum- 

 stances may act happily on inert plant food 

 in the soil and render it assimilable. In 

 this respect it doubtless can assist greatly 

 in plant growth. In respect of the mineral 

 food of plants it may be said that it appears 

 to be of two kinds : First, the minerals 

 which are essential, such as phosphoric 

 acid, potash, lime and magnesia. A certain 

 quantity of these mineral substances seem 

 to be necessary for the production of a 

 given quantity of dry plant tissue. But 

 plants have also a general appetite for min- 

 eral substances, eating freely in addition to 

 the quantity necessary to their proper nu- 

 trition. The exact physiological function 

 of this excess of mineral food cannot be de- 

 termined, and it is probable that it is largely 

 accidental. ISTevertheless, recent investiga- 

 tions have shown that plants thrive best 

 where mineral food, even when non-essen- 



tial, is liberally supplied, and in these cases 

 soda doubtless plays its part, together with 

 other non-essential matter. 



In the light of our present knowledge, 

 however, it must be denied that soda can, 

 in any essential way, replace potash in 

 plant growth. 



In a recent re- study of the proteids of 

 the maize kernel, Osborne has brought 

 practically to a close his interesting and 

 valuable contributions to our knowledge of 

 the proteid matters existing in many com- 

 mon cereals. In a sample of yellow maize 

 meal he finds 3.15 per cent, of a proteid 

 soluble in a 0.2 per cent, solution of potash. 

 This proteid contains 15.82 per cent, of 

 nitrogen. The quantity of zein is 5 per 

 cent., containing 16.32 per cent, of nitro- 

 gen. These two proteids comprise almost 

 the whole of the proteid matter in the 

 maize. In addition to these, there are 

 minute quantities of edestin containing 

 18.10 per cent, of nitrogen ; a globulin, 

 containing 15.25 per cent, of nitrogen, and 

 a proteose, containing 17 per cent, of nitro- 

 gen. Maysin exists to the extent of one- 

 quarter of one per cent, and contains 16.70 

 per cent, of nitrogen. 



As a result of. all the determinations, it 

 appears that the mean percentage of nitro- 

 gen in the proteids of maize is 16.057. 



The proper factor for the multiplication 

 of proteid nitrogen to determine the total 

 weight of proteids in maize is, therefore, 

 6.22. This is so near the common factor 

 of 6.25 as to make practically little differ- 

 ence in the statement of results. The fac- 

 tors by which nitrogen should be multiplied 

 in order to obtain the weights of proteids 

 in common cereals are: for wheat, 5.70; 

 rye, 5.62 ; maize, 6.22 ; oats, 6.06, and 

 barley, 5.82. This revision of the factors 

 for determining the total amount of pro- 

 teid matter is not only important as regards 

 this matter itself, but also affects the num- 

 ber for the determination of the carbohy- 



