292 



SCIENCE 



[N. S. Vol. XXXIX. No. 



fused with the basal margin of the leaf and the 

 lateral margin of the stem (stipe) just where this 

 unites with the leaf. 



The vertical restriction upon axial growth is 

 found to limit the development of new parts to the 

 horizontal plane, and successive outgrowths are 

 produced as lateral developments rather than in a 

 vertical succession as in normal erect stems. No 

 new parts are found, but those present have under- 

 gone reduction as a result of adaptation to the 

 floating habit. 

 Development of the Embryo and the Germination 



in Lemna perpusilla: Frederick H. Blodgett. 



The embryo of Lemna develops directly from 

 the egg cell, all of which is involved in the forma- 

 tion of the embryonic tissues, a true suspensor not 

 being differentiated. The plumule becomes folded 

 against the hypocotyl so that its tip is just under 

 the micropyle. In this position it is enclosed by 

 the overgrowth from the base of the cotyledon, 

 forming a sheath or pouch. At the base of the 

 plumule a bud is developed, which is the first true 

 frond, and this bears the first pair of buds char- 

 acteristic of the dichasial branching of the plant. 

 The anterior half of the embryo is the cotyledon, 

 and acts as an haustorial organ during germina- 

 tion, and does not function otherwise. The 

 plumule emerges from the sheath from a horizontal 

 slit, thus lying from the first in the plane of the 

 water surface. The germination of the seed is in 

 general of the type of Pistia, differences being due 

 to the greater degree of reduction in the case of 

 Lemna, rather than inherent variations in method. 



The Chemical Dynamics of Living Protoplasm: 



W. J. V. OSTERHOUT. 



Van't Hoff's formulation of the laws of chem- 

 ical dynamics has proved so stimulating to various 

 fields of chemistry that it may be expected to be 

 similarly useful if it can be applied to the activi- 

 ties of living protoplasm. The writer finds that 

 by measuring the electrical resistance of living 

 tissues it is possible to follow the progress of reac- 

 tions in protoplasm in the same way that van't 

 Hoff followed the progress of reactions in vitro. 

 It therefore becomes possible to apply van 't 

 Hoff's methods and formulas directly to proto- 

 plasm in its living and active condition. The fol- 

 lowing example will suffice to show how this may 

 be accomplished. 



The electrical resistance of living tissue of 

 Lammwjria was measured by a method which has 

 been previously described. The tissue had in sea- 

 water a resistance of 980 ohms. On being placed 



in NaCl .521VI (which had the same conductivity as 

 sea-water) the resistance fell after 10 minutes to 

 865 ohms and after 20 minutes to 745 ohms : it 

 continued to fall rapidly and finally became sta- 

 tionary at 320 ohms. This represents the death- 

 point. The total change produced by the NaCl 

 was 930 — 320 := 660 ohms. In order to find out 

 whether this change had been produced in such a 

 way as to correspond to a kno-nm type of chemical 

 reaction the amount of change was measured at 

 brief intervals. 



According to van't HofC we can determine from 

 such measurements whether one, two or more sub- 

 stances are taking part in the reaction. If only 

 one substance takes part (or if two substances 

 take part but only one of them changes its con- 

 centration noticeably) the reaction is said to be of 

 the first order (monomoleeular) and it proceeds 

 according to the formula 



1 a 



A- = T log. , 



i a — X 



in which t is the time which has elapsed between 

 the beginning of the reaction and the taking of 

 the measurement, x is the loss in resistance at the 

 time *, a is the total amount of change in re- 

 sistance when the reaction is completed and fc is 

 a constant (called the velocity constant) which 

 indicates the speed of the reaction. If the reac- 

 tion is of the first order (monomoleeular) Tc 

 should come out constant provided the tempera- 

 ture be kept constant during the reaction. 



In this ease a, which represents the total amount 

 of change, is 980 — 320 = 660 ohms, while x rep- 

 resents the loss of resistance after 10, 20, 30 

 minutes, etc. The calculations show that Tc is 

 nearly constant: the variations are no greater than 

 are commonly foimd in measuring chemical reac- 

 tions in the test-tube. 



Since the effect of NaCl is within wide limits 

 completely reversible, without production of in- 

 jury, the conception of chemical dynamics here de- 

 veloped applies not only to reactions which pro- 

 duoe death, iut also to reactions which involve no 

 injury and which form a normal part of the ac- 

 tivity of the cell. This conclusion is fully eon- 

 firmed by experiments with a variety of other sub- 

 stances. 

 A Contribution to the Theory of Antagonism: W. 



J. V. OSTERHOUT. 



By means of electrical measurements of living 

 tissues it is possible to predict which salts wiU an- 

 tagonize each other when allowed to act upon these 

 tissues. 



