SENECIO VULGARIS. 241 



would be a serious impediment to its increase. Mr. Darwin, in 

 the same chapter to which I have already referred, instances a 

 plant oi Lobelia fidgens in his garden, which absolutely will not pro- 

 duce seed unless visited by insects ; but as in his locality he knows 

 it is not so visited, he compromises the matter, and insures his 

 seedlings by crossing the pollen with his own hands. He dwells 

 further upon the mutual checks to increase, remarking that 

 plants and animals are bound together by a web of complex 

 relationship. He believes that the Heart's-ease ( Viola tricolor) and 

 the Red Clover ( Trifolhwi pratense) are wholly dependent for their 

 existence upon the visits of Humble-Bees, other bees not visiting 

 these flowers. If the Humble-Bee became extinct, he believes that 

 these plants would become extinct also. 



Now, the Humble-Bees increase or decrease in inverse propor- 

 tion to the number of field-mice found in the same district, as these 

 animals destroy their nests and combs : one naturalist affirms that 

 throughout England two-thirds of the Humble-Bees are thus des- 

 troyed : and, lastly, the number of field-mice depends on the 

 number of cats. The same naturalist affirms that near villages 

 and towns the number of Humble-Bees is greater than in the open 

 country, because the cats (as we in Bath know by painful experi- 

 ence) are more numerous. Darwin, therefore, adds — " It is quite 

 credible that the presence of feline animals in large numbers in a 

 district might determine, through the intervention, first of mice, 

 and then of bees, the frequency of certain flowers in that district." 

 Hence the peculiar self-fertilising character of the flowers of 

 Senecio vulgaris is an additional cause for the favourable increase 

 of the plant. 



To recapitulate, then, we have three very important causes 

 which prevent the extinction of the Groundsel : — 



I. — Parachute, or " plumed " seeds, which insure distribution. 



2. — Vast seed-bearing qualities. 



3. — Self-fertilisation, which renders the plant indifferent to the 

 visits of insects. 



As to the dissemination of these plumed seeds by the agency 

 of the wind, Mr. H. J. Slack, in his paper on " Plant-Hairs," in 

 Science for All, narrates an interesting fact which came under his 

 own observation. When looking through an astronomical tele- 



