GROWTH, METAMORPHOSIS AND DEVELOPMENT 267 



tioned, how cell division results, what are the relations between 

 nucleus and cell protoplasm, are questions which are not yet ripe 

 for colloid research. 



To be sure we know that such swelling and shrinking processes 

 occur, not only for the entire cell, but also in the nucleus. Before 

 each cell division the nucleus swells up very much, and after division 

 shrinks again, decidedly. 



BOROWIKOW* made interesting observations on plant growth. All 

 who are familiar with plants know that even in summer, periods of 

 apparent rest alternate with periods of active growth (sprouting). 

 The latter phase is associated with considerable entrance of water. 

 It is impossible to explain this imbibition of water by osmotic forces 

 since the increased rate of growth was usually associated with a 

 diminution in the concentration of the cell juices instead of the 

 reverse, and a growing plant absorbed unequal quantities of water 

 from solutions osmotically identical. There was, on the contrary, 

 some evidence that swelling processes were active. MARTIN H. 

 FISCHER had already called attention to the fact that the tips of buds 

 are always acid in reaction. It was quite natural, therefore, to test 

 the influence of acids, bases and salts on the sprouting of plants and 

 to compare it with the swelling of colloids. For this purpose BORO- 

 WIKOW placed six-day old sunflower seedlings (Helianthus ammus) 

 in sieves and dipped them in various solutions, using distilled water 

 as a control. 



Dilute acids (1/100 normal) accelerated growth while salts simul- 

 taneously present acted against the acids. Acids and salts were 

 active in a series which was analogous to that for the swelling and 

 shrinking of dead colloids. 



That bases caused no acceleration of sprouting seems to militate 

 against the original assumption. BOROWIKOW explains this by the 

 fact that the cell juice in the growth zone is essentially acid and con- 

 stantly forms carbonic acid; the bases neutralize the acid, forming 

 neutral unhydrated albumin and in higher concentrations damage 

 the plants. In this way he explains the stimulating action of dilute 

 solutions of organic bases (0.001 n urea nitrate, 0.0015 n caffein 

 sulphate, 0.0025 n phenylene diamine chlorid) which, according to 

 BOROWIKOW, act like their respective acids since they are hydrolyzed 

 in solution. 



BOROWIKOW expects especially to bring growth into relationship 

 with turgor (tissue distention). Unnoticed, great turgor may be 

 diminished by the growth process. According to BOROWIKOW 

 growth is ionization of the plasma protein by H ions in the growth 

 zone, causing the protein to pass from the gel to the sol condition. 



