20 THE QUANTITATIVE METHOD IN BIOLOGY 



This is the ordinary rule in nurseries.^ What is the influence 

 of the new state of things on plasticity, the material being 

 monotypic (a monotypic species or a subspecies) ? 



Under the new conditions certain reactions of the living 

 substance of the species are modified ; certain properties and 

 even the facies are altered. In the successive experiments 

 various alterations occur. We say that the species varies or is 

 beginning to vary under cultivation. This is a misuse of terms. 

 The faculty of varying, which depends on the specific living 

 mixture, is not modified ; only the visible properties are 

 deviating from their previous state. 



EXAMPLE : In the state of nature the length of the in- 

 florescence (spike-like panicle) of Phleum pratense, for instance, 

 varies ordinarily between 2 and 10 cm. (proportion, 1:5; 

 mean length, 6 cm.), the extremes being uncommon. In a 

 given garden the limits are, for instance, 3 and 15 cm. (propor- 

 tion, 1:5; mean length, 9 cm.), the extreme values being 

 easily found, since numerous specimens are growing on a small 

 area. The absolute value of the difference between the limits 

 is increased, and therefore we may have the impression that 

 the species is more inclined to vary, although the degree of 

 plasticity, considered as a specific property, is not modified.^ 

 (It is moreover possible to find under natural conditions speci- 

 mens the inflorescence of which has a length equal or even 

 superior to that of the longest inflorescence observed under 

 cultivation.) 



§ 25.— VARIATION UNDER CULTIVATION. MONO- 

 TYPIC SPECIES {continued). NEW PROPERTIES.— Under 

 given conditions certain possible reactions of a species do not 

 take place, the corresponding properties being latent (§ 10) . I 

 take as example the fasciation of the stem. Suppose that a 

 species in which fasciation has never been observed under 

 natural conditions is cultivated in a garden. It may happen 

 that a number of stems become more or less fasciated. In this 

 case it seems to be unquestionable that variability has been 

 augmented by cultivation, ^ for a new property has appeared, 



^ If it seems impossible to obtain healthy, vigorous (commercial) plants, the 

 experiment is abandoned. Failures are very rarely published or even men- 

 tioned, and we are told nothing about variation under unfavourable con- 

 ditions. 



* The possibility that altered conditions of existence may really modify 

 temporarily the degree of plasticity (by altering the quantitative composition 

 of the living mixture ; see § 8a) is not excluded a priori, but we have no 

 exact information about this . It is only by delicate experiments and by the 

 use of the quantitative method that an answer to this question can be 

 found. 



^ Using a well-known expression, we might say that the species has gone 

 mad {Pespece est affoUe). 



