238 Influence of Environment on Plants 



flowers by varying the time at which the stimulus is applied, and by 

 the cooperation of other factors such as temperature, darkness, etc. 

 In number and arrangement the several floral members vary within 

 wide limits ; sepals, petals, stamens, and carpels are altered in form and 

 colour, a transformation of stamens to carpels and from carpels to 

 stamens occurs in varying degrees. The majority of the deviations 

 observed had not previously been seen either under natural con- 

 ditions or in cultivation ; they were first brought to light through the 

 influence of external factors. 



Such transformations of flowers become apparent at a time, which 

 is separated by about two months from the period at which the 

 particular cause began to act. There is, therefore, no close con- 

 nection between the appearance of the modifications and the external 

 conditions which prevail at the moment. When we are ignorant of 

 the causes which are operative so long before the results are seen, 

 we gain the impression that such variations as occur are spontaneous 

 or autonomous expressions of the inner nature of the plant. It is 

 much more likely that, as in Sempervivum, they were originally 

 produced by an external stimulus which had previously reached the 

 sexual cells or the young embryo. In any case abnormalities of this 

 kind appear to be of a special type as compared with ordinary 

 fluctuating variations. Darwin pointed out this difference; Bateson 1 

 has attempted to make the distinction sharper, at the same time 

 emphasising its importance in heredity. 



Bateson applies the term continuous to small variations connected 

 with one another by transitional stages, while those which are more 

 striking and characterised from the first by a certain completeness, 

 he names discontinuous. He drew attention to a great difficulty 

 which stands in the way of Lamarck's hypothesis, as also of Darwin's 

 view. " According to both theories, specific diversity of form is 

 consequent upon diversity of environment, and diversity of environ- 

 ment is thus the ultimate measure of diversity of specific form. 

 Here then we meet the difficulty that diverse environments often 

 shade into each other insensibly and form a continuous series, 

 whereas the Specific Forms of life which are subject to them on the 

 whole form a Discontinuous Series." This difficulty is, however, not 

 of fundamental importance as well authenticated facts have been 

 adduced showing that by alteration of the environment discontinuous 

 variations, such as alterations in the number and form of members 

 of a flower, may be produced. We can as yet no more explain 

 how this happens than we can explain the existence of continuous 

 variations. We can only assert that both kinds of variation arise in 

 response to quantitative alterations in external conditions. The 



1 Bateson, Materials for the study of Variation, London, 1894, p. 5. 



