IN THE DIVIDING ROOT-TIP CELLS OF THE ONION. 39 



(6). VAN'T HOFF'S LAW. 



If van't Hoff's principle is taken to apply only to simple chemically 

 homogeneous reactions, it finds little direct application to the measure- 

 ments herein reported for the influence of temperature-increments 

 upon mitotic velocity. However, determining the Qio values, i. e., the 

 coefficients for simple or complex physical, chemical, or physiological 

 activities, is a very useful method of analysis. But when we find 

 Qio values of the magnitude of van't Hoff's expectation, namely, of 

 from +2.0 to +3.0, we must not consider therefore that we have of 

 necessity located a simple homogeneous chemical reaction. We may 

 or we may not have found such. As many as possible of the con- 

 tributing factors must be taken into consideration and each duly 

 weighted. Every chemical and physical activity has its characteristic 

 velocity-response to a 10° C. rise in temperature. Generally these val- 

 ues vary from —2.0 to +5.0. Because in these experiments with mito- 

 sis the value of Qio is never greater than +4.95 and never less than 

 — 1.18, the evidence points strongly toward the nature of mitotic 

 forces being chiefly chemical and physico-chemical, but without 

 further analysis this evidence tells little more as to what combina- 

 tion of a great repertoire of activities may be involved in the mitotic 

 stage-complex whose activities are measured as a unit. 



The fact that influences are both specific and measurable is the 

 encouraging thing. The measuring of two complexes differing only in 

 one factor supphes a measure of this differential. If finally a vital 

 reaction is analyzed and one of its elements closely accords in behavior 

 with some simple reaction, well and good, for such indicates approach 

 to the elementary, and elemental formulas relating to such a 

 complex can be synthesized; but calling a patently and unanalyzed 

 complex elementary because it responds like such in one or more 

 respects hardly makes for progress. Doubtless the component proc- 

 esses of mitosis are of a chemical and physico-chemical nature and 

 their individual responses to temperature-changes are of the expected 

 nature and degree. But the interplay of activities may cause the 

 complex as a unit to synchronize with certain selected elements or the 

 conflict of forces may greatly retard or accelerate the common progress. 

 For instance, the production of enzyme A may be proceeding at a 

 chemically expected rate in response to its surrounding temperature. 

 But when enzyme A comes in contact with enzyme B, which is being 

 similarly produced, their interaction may introduce another factor, 

 accelerating or retarding general or specific progress. Also, anti- 

 catalysis (or the influencing of the velocity of production of a chemical 

 product by the unremoved product itself) is a factor. It is a mass of 

 such individual activities that we measure in most physiological 

 activities, and especially is this true in mitosis. 



