349 



is tliat thoy aro to be ascribed to (bttcioiiccs in the i)ro(bi('tivo energy 

 oi' tlic iii(li\i(Iiial ]>laiits. Here, in AVohltmanu's jiulgnieiit, lies the 

 ('liid' (iiriiculty in the way of exaet experiinentiiig with plants on a 

 small scale. The iiulivichiality of the ])lants is the one factor which is 

 beyond contri*!. The oidy way to avoid its disturbing influence is to 

 increase the nnniber of i)laiits and take the average results. It is to 

 be notetl, li(»\\ CN cr, that the variations from the mean of the duplicates, 

 vvhicli wonhl be <nily about one half the above percentages, average 

 only 2.L' per cent, that they exceed 5 per cent in only four cases, and 

 that tln-y reacli only 7.7 in the worst case of all. This range of jn'ob- 

 abU' error is not legarded by the author as suflicient to seriously aft'ect- 

 the value of ex]»eriments for ordinary purposes, and hence in this 

 respect theniethod is regarded by him as satisfactory. Boxes of the 

 sizeof those used by Wohltniann, with 0.4-meter area, have the advantage 

 over Wagner's smaller cylimlers that they hold more plants, and thus 

 decrease the error due to difference of individuality of plants. 



As a means of avoiding the difficulty of disagreement of duplicates, 

 Wohltnnmn urges the importance of several parallel trials — triplicates 

 at least, and more if convenient. Another advantage of the larger 

 number is that if the plants in one box are injured the experiment is 

 not spoiled. 



(.)) NN'ohltmann claims as further advantages of the boxes sunk in the 

 earth as compared with Wagner's small cylinders above the surface of 

 tlie soil, that the conditions are more nearly nornml; the observations 

 of drainage water are valuable; and the time, labor, care, and conline- 

 ment required of the exijerimenter are not half as large. [The reason 

 for the last-named difference is that Wagner's pots have to be weighed 

 \ery often, in the time of rapid growth of the plants once or even 

 twice a day, in order to determine the amount of water Avhich must be 

 given to keep the soil properly moist, and that the attendant must 

 be constantly on hand to put the plants under cover when a storm is 

 imminent, while in Wohltmann's boxes the Avater supply can be regu- 

 hited by keeping the water table at the desired level, and no constant 

 attention is otherwise required.] On the other hand, Wagner's i)lan of 

 keci>ing the ]iots on small platform cars beside a glass Inmse, into which 

 they are easily run, gives very valuable protection against frost and 

 storms, e. //., severe rain or hail, which may sometimes ruin a whole 

 season's work. 



(4) While Wohltmann recognizes the incompleteness of our present 

 methods for physical and chemical studies of the soil, he still urges their 

 great inqxtrtance for investigations of this class. 



In conclusion, the author calls attention to the usefulness of the boxes 

 described by him for educational purposes. They offer a very conven- 

 ient means for demonstration of experiments, and might be advanta- 

 geously used by agricultural schools, especially those which have not 

 adequate held and garden area. — [W. O. A.] 



