274 



EVOLUTION 



lar and often fantastic forms and excep- 

 tional structure to special adaptations 

 for cross-fertilization bv insects, with- 

 out the agcnc\- of which most of them 

 would be absolutely sterile. It became 

 evident that ever)' peculiarity of these 

 wonderful plants, in form or structure, 

 in colour or marking, in the smooth- 

 ness, rugosity, or hairiness of parts of 

 the flower, in their times of opening, 

 their movements, or their odours, had 

 every one of them a purpose, and were, 

 in some way or other, adapted to se- 

 cure the fertilization of the flower and 

 the preser\'ation of the species. 



RESEARCHES ON THE COWSLIP, 

 PRIMROSE, AND LOOSESTRIFE 



The cowslip {Primula veris) has 

 two kinds of flowers in nearly equal 

 proportions: in the one the stamens 

 are long and the style short, and in the 

 other the reverse. This fact had been 

 known to botanists for seventy years, 

 but had been classed as a case of mere 

 variabilit}-, and therefore considered to 

 be of no importance. After a consider- 

 able amount of observation and experi- 

 ment, Darwin found that bees and 

 moths visited the flowers, and that their 

 probosces became covered with pollen 

 while sucking up the nectar, and fur- 

 ther, that the pollen of a \ong-stamened 

 plant would be most surely deposited 

 on the stigma of the \ong-styled plants, 

 and vice versa. 



Tlie same thing was found to occur 

 in the primrose, and in many other 

 species of Primulaceae, as well as in 

 flax, lungworts, and a host of- other 

 plants. 



Still more extraordinary is the case 

 of the common loosestrife {Lythrum 

 salicaria ) , which has both stamens and 

 st}les of three distinct lengths, each 

 flower having two sets of stamens and 

 one style, all of different lengths, and 

 arranged in three different ways: (1) 

 a short style, with six medium and six 



long stamens; (2) a medium style, with 

 six long and six short stamens; (3) a 

 long style, with six medium and six 

 short stamens, 'f'hese flowers can be 

 fertilized in eighteen distinct ways. The 

 exact correspondence in the length of 

 the style of each form with that of the 

 stamens in the two other forms ensures 

 that the pollen attached to anv part of 

 the body of an insect shall be applied 

 to the style of the same length in 

 another plant, and thus there is a triple 

 chance of the maximum of fertility. 



THE STRUGGLE FOR EXISTENCE 



But we must pass on from these 

 seductive subjects to give some indica- 

 tion of the numerous branches of in- 

 quiry' of which we have the results 

 given us in the Origin of Species, but 

 which have not yet been published in 

 detail. The observations and experi- 

 ments on the relations of species in a 

 state of nature, on checks to increase 

 and on the struggle for existence, were 

 probably as numerous and exhaustive 

 as those on domesticated animals and 

 plants. As examples of this we find 

 indications of careful experiments on 

 seedling plants, and weeds to deter- 

 mine what proportion of them were 

 destroyed by enemies before they came 

 to maturity; while another set of ob- 

 servations determined the influence of 

 the more robust in killing out the 

 weaker plants with which they came 

 into competition. The rare and deli- 

 cate flower which we find in one field 

 or hedgerow, while for miles around 

 there is no trace of it, maintains itself 

 there, not on account of anv specialty 

 of soil or aspect, or other physical con- 

 ditions being directly favourable to it- 

 self, but because in that spot only there 

 exists the exact combination of other 

 plants and animals which alone is not 

 incompatible with its wellbeing. Such 

 considerations teach us that the var)'- 

 ing combinations of plants character- 



