38 THE QUANTITATIVE METHOD IN BIOLOGY 



In some examples the existence of intermediate properties 

 depends obviously on environmental influences. (BATESON, 

 loc. cit., p. 243.) For instance, the cotyledons of many sub- 

 species of peas are in all ripe seeds a full yellow, while those of 

 many others are a full green. The contrast between the pro- 

 perties yellow and green in Fg (after segregation) may be 

 perfectly sharp and clear. Some subspecies, however, have many 

 seeds which are in various degrees partly yellow and partly 

 green. I have observed that it is sometimes possible to bring 

 a number of seeds into a series from about full yellow to about 

 full green in such a way that the difference between two succes- 

 sive seeds is very slight. In such a case, if we overlook the 

 fundamental distinction between possibility and property,^ the 

 existence of a gradual passage between the extremes seems to 

 be incontestable. BATESON, after experimenting with such 

 kinds, found that the parti-coloured appearance was caused by 

 exposure to sun and weather. Plasticity is here in play, but 

 no intermediates exist with regard to the possibilities, although 

 the latter may coexist in the hybrids. 



In other cases an intermediate property is observed in the 

 hybrids Fj and transmitted to the generations F2, F3 . . . 

 without segregation. 



EXAMPLE : The subsequent generations raised from the 

 hybrids (Enothera muricata x CE. biennis showed no definite 

 departure from the Fj type.^ 



If this and other similar examples are not susceptible of any 

 other explanation, the suggestion may be accepted that here a 

 new, quite distinct living mixture H has been brought into 

 existence and that therefore a new property H has appeared, 

 the new mixture differing from the ordinary hybrid mixture 

 because it finds itself in a state of stable equilibrium which is 

 permanent and transmissible by heredity. ^ (Constant hybrid.) 



In other words, according to this view, a new subspecies H 



^ In other words, between chemical constitution and observable reaction. 



2 HUGO DE VRIES, die Mutationstheorie (Leipzig, Veit & Co., 190 1), vol. i., 

 p. 67. In several successive generations the hybrid alluded to was constant, 

 on the whole differing little from (E. biennis. The middle radical leaves 

 of the hybrid were similar to those of CE. biennis and distinctly different from 

 those of CE. muricata by their length, breadth, form, border and nerves. (See 

 also BATESON, loc. cit., pp. 249-250.) 



^ This may be rendered more intelligible by the following comparison : — 

 when a fixed oil is mixed with water the mixture is in a state of unstable 

 equilibrium : after a certain time segregation takes place and both components 

 are separated. This corresponds to an ordinary hybrid mixture. When a 

 fixed oil is mixed with ether the mixture becomes a solution, which is in a 

 state of stable equilibrium and therefore permanent, without segregation. 

 This is comparable to the supposed mixture H and also to any ordinary 

 specific (not hybrid) mixture. It is conceivable that a similar principle finds 

 application in the living mixtures, although these mixtures are very com- 

 plicated. 



