78 TKANSACTIONS, NATURAL HISTORY SOCIETY OF GLASGOW. 



form assumed by the pappus has probably in most 

 cases some relation to the habits of the species. A 

 plumose pappus is perhaps better adapted for trans- 

 port, but the pilose form offers less resistance when 

 the seed has to penetrate a mass of vegetation 

 before reaching the soil. On the whole, the append- 

 ages of seeds will tend to assume the form best 

 fitted to secure their delivery in situations such as 

 are usually preferred by the species. The differences 

 observed in the pappus of Compositse correspond in 

 all likelihood with differences in their habitats. The 

 adaptation to wind-dispersion is in many plants of 

 this order carried to great perfection. In some 

 instances it almost seems as if the development of the 

 pappus were of equal importance with the arrange- 

 ments for the fertilisation of the flowers, so elaborate 

 are the precautions to prevent injurj"^ and to insure 

 that the plumes of the seed shall attain their proper 

 condition at the period of ripening. During the 

 early stages of maturation the bracts of the invo- 

 lucre are vertical, and securely enclose the capitulum, 

 which almost re-assumes the appearance it had in 

 the bud before the flowers expanded. Tussilago even 

 inverts its capitulum until the fruit is ripe, when 

 the flower-head again becomes erect so that the 

 pappus may more readily catch the wind. No one 

 who has closely observed the thistle-down can 

 readily forget it, so beautiful are its silky plumes 

 and so admirably fitted to fulfil their purpose. If 

 a flower head in course of ripening be opened, each 

 separate fruit is seen to be tipped with a pencil of 

 long silky hairs. Somewhat later these begin to 

 separate and spread in all directions. Just then the 

 connection below with the receptacle is loosened, 

 and the spreading of the hairs has the effect of 

 raising the seed out of the cup-like capitulum. A 

 certain number of the hairs are even directed down- 

 wards, their points resting on the floor of the 

 receptacle. At first these vertical hairs are not 

 straight, but wavy; and, as they straighten, the 



