May 18, 1917] 



SCIENCE 



487 



water, while it is invariably less in alkaline 

 than in acidified solutions. The interest in 

 swelling' which begins with a neutral desic- 

 cated section is, however, much less than that 

 which attaches to the behavior of such mate- 

 rial under changing conditions of alkalinity 

 and acidity which are taken to occur in the 

 living plant. 



Dried plates of agar-protein, agar-tyrosin 

 and agar-cystin .12 to .25 mm. in thickness 

 and 3 by 4 or 5 mm. were placed in trios on 

 the bottoms of stender dishes. Triangular 

 pieces of glass were placed to cover the sec- 

 tions of colloid in each dish and an auxograph 

 was arranged to give a bearing contact of the 

 swinging arm on a socket in the center of the 

 triangular plate. So long as the preparation 

 remained in this condition the pen of the in- 

 strument traced a horizontal line on the sheet 

 carried by the drum. Dried sections of the 

 colloids have a very limited capacity for imbi- 

 bition of acid and alkaline solutions, and hence 

 it was desirable to start swelling or " growth " 

 by an initial immersion of an hour in distilled 

 water, which was poured in the dishes. After 

 enlargement had begun hundredth-normal acid 

 or alkaline solutions were used in alternation 

 at intervals of one to three hours, as many as 

 four changes being made in some cases before 

 the total swelling capacity was reached. The 

 results met all expectations based on theoret- 

 ical considerations and the auxographic trac- 

 ings might easily be mistaken for records of 

 the variations of the length of a joint of 

 Opuntia, for example. 



Sections of plates 90 parts agar to " 10 " of 

 tyrosin gave a tracing traversing 12 mm. ver- 

 tically on the record paper during the first 

 hour immersed in distilled water, remained 

 stationary, making a horizontal line during 

 the second hour, the water having been re- 

 placed with hundredth-normal hydrochloric 

 acid, traversed 11 mm. of the scale in the 

 third hour during which it was immersed in 

 hundredth-normal sodium hydrate, then shrunk 

 5 mm. in an hoiir in acid, then enlarged 9 mm. 

 in three and a half hours in alkali, after 

 which it shrunk 3 mm. between 8 :30 p.m. and 

 7 A.M. in acid. A change to alkali gave an 



enlargement of 6 mm. in two hours. The 

 auxograph was set to multiply so that the 

 actual enlargement in the periods noted was 

 one twentieth of the distance traversed by the 

 pen. The change from acidity to alkalinity 

 is followed by the most marked effects when 

 the colloid has taken up a fourth or a third of 

 the possible total amount of water. Perhaps 

 the most striking feature is the response of 

 the colloid to acidification under the alter- 

 nating conditions. Desiccated sections give a 

 greater total swelling in acid than in alkali, 

 but when a certain amount of swelling has 

 already taken place under neutral or alkaline 

 conditions no further increase in acid solu- 

 tions takes place and actual shrinkage ensues. 

 A change to alkalinity is always followed by 

 increased imbibition. 



The experiment in question has many fea- 

 tures similar to those of the plant. Changes 

 from alkalinity to acidity and the reverse must 

 be made quickly to avoid instrumental error, 

 consequently some acid or alkali is not re- 

 moved from the dish. The plate of swelling 

 colloid is saturated with the liquid which is 

 being removed and neutralization, acidifica- 

 tion or the reverse does not occur for some 

 time. Such conditions prevail in the plant 

 and come about even more slowly. 



The disintegration of the acid of Opuntia 

 beginning at daybreak does not overtake the 

 formation of this substance until as late as 4 

 P.M. Whether complete neutralization or alka- 

 line conditions ever occur in this plant is 

 doubtful. There is ground for the assimap- 

 tion that it does in other plants, however. 



The almost rhythmic undulations of the 

 ausographic tracing of the elongation of a 

 wheat leaf corroborated by measurements 

 with the horizontal microscope suggest that 

 growth in this organ may be accompanied by 

 metabolic processes by which the balance of 

 acidity and alkalinity falls now on this and 

 then on that side, there being of course pos- 

 sible periods in which the growing protoplasts, 

 or some of them, were in a neutralized state. 

 During this time, of course, imbibition might 

 be four to eight times as great as in either 

 acid or alkaline conditions. 



