322 



WITH PLANTS 



ming over its surface at a high rate of speed, and 

 every footprint is soon carpeted with them. On the 

 plains the Eussian Thistle and other "tumble- 

 weeds" are blown over the level surface of 

 the ground, scattering their seeds at every 

 step (in this case the whole plant assists in 

 the dissemination). 



The problem of flying is solved in various 

 ways : sometimes the calyx is modified into a 

 parachute (Dandelion, Thistle, etc.) ; some- 

 times the style (Clematis, Fig. 171) is used 

 for this purpose; a bract may serve as a 

 wing (Linden, Fig. 172, and Hop, Fig. 173), 

 or the wall of the ovary may grow out into a 

 flattened wing - like appendage 

 (Maple, Fig. 174) , while in other 

 cases it is the seed -coat which 

 grows out in this way 

 Find out what you can 

 about this. A very simple 

 way of testing the effec- 

 tiveness of these flying de- 

 vices is to drop the seeds 

 from a height down a stair 

 well or wherever the air is 

 still, and time them in 

 their fall to the earth. 



attach- 172t Linden fruit - which flies 



aitacn- of a wing . like bract . 



171. Clem- 

 atis fruit, 

 which flies 

 by means 

 of the 

 feat hery 

 style. 



(Pines) 



