22 THE QUANTITATIVE METHOD IN BIOLOGY 



been increased by cultivation, although the observed facts are 

 simply a consequence of the laws of hybridization. 



§ 27.— VARIATION UNDER CULTIVATION {continued). 

 COMPLEX SPECIES. LATENT PROPERTIES.— It may 

 happen that a species which is in fact complex has been 

 hitherto considered monotypic, because the characteristic 

 properties of one or several of its subspecies are practically 

 always latent under natural conditions.^ HUGO DE VRIES 

 has demonstrated, by means of numerous admirable experi- 

 ments, that a number of so-called monstrosities (anomaUes) 

 are peculiar subspecies (DE VRIES calls them races) . Certain 

 of them are exceedingly rare in the state of nature, but in a 

 garden they are obtained in numerous specimens when culti- 

 vated under very favourable conditions. In the same garden 

 their characteristics become again latent whenever the condi- 

 tions (manure, etc.) become less favourable. 



I take as an example Dipsacus silvestris. Although this species 

 is common in Europe, very few botanists have seen a specimen 

 of subspecies torsus DE VRIES, characterised by a twisted 

 stem ; it has probably never been mentioned in any flora. ^ 

 HUGO DE VRIES, starting from the seed of one specimen, 

 cultivated this plant for years and succeeded in obtaining an 

 unlimited number of specimens as often as the conditions of 

 existence were very favourable. In the most favourable cases 

 about 30 per cent, of the cultivated specimens were twisted. ^ 



Suppose now that a sample of seed taken at random from 

 ordinary specimens (which do not exhibit any visible trace of the 

 properties of subspecies torsus) was used to start a culture, and 

 that we were quite ignorant of the experiments of DE VRIES 

 and even of the existence of twisted stems. If one of the 

 parental plants happened to be a torsus with latent properties, 

 or if one seed was fertilized by a pollen grain from a latent 

 torsus, it might happen that in the garden, in the first or in a 

 subsequent generation, one or several specimens would exhibit 



^ Compare § 25 (latent properties of a monotypic species). 



2 1 have observed thousands of specimens of D. silvestris in Flanders (Nieu- 

 port, Ostend, Blankenberghe, Ter Neuzen, etc., on clayey soil without lime- 

 stone) and in the valley of the Meuse (between Huy and Namur, on rather 

 clayey soil, limestone district). I did not succeed in finding a single specimen 

 of the handsome subspecies torsus, although its characteristics are very 

 apparent. 



^ Some years ago Prof. H. DE VRIES kindly sent me some seeds of his 

 D. silv. torsus. Thirty-one plants were obtained and carefully cultivated on a 

 bed in the Botanic Garden at Ghent by the head gardener, J. V. BURVENICH. 

 Unfortunately the spaces between the plants were too small. This is very 

 probably the reason why only one twisted specimen appeared. It grew at a 

 corner of the bed, under better conditions than the others, because it there 

 found plenty of space for its development. Seed was collected by Mr J. V. 

 BURVENICH, who unfortunately fell ill and died soon afterwards. After his 

 death the seed was not found. 



