118 



PLANT RELATIONS. 



Fig. 122. A fruit of witch 

 hazel discharging its 

 seeds.— After Beal. 



light or sandy soil (see Fig. 120). 

 When the work of the season is over, 

 and the absorbing rootlets have 

 shriveled, the plant is easily blown 

 from its anchorage by a gust of wind, 

 and is trundled along the surface like 

 a light wicker ball, the ripe seed ves- 

 sels dropping their seeds by the way. 

 In case of an obstruction, such as a 

 fence, great masses of these tumble- 

 weeds may often be seen lodged 

 against the windward side. 



79. Discharge of spores. — In many 

 plants the distribution of spores and 

 seeds is not provided for by any of 



the methods just mentioned, but the vessels containing 



them are so constructed that they are discharged with 



more or less violence and are some- 

 what scattered. 



Many spore cases, especially those 



of the lower plants, burst irregularly, 



and with sufficient violence to throw 



out spores. In the liverworts pecu- 

 liar cells, called elaters or "jumpers," 



are formed among the spores, and 



when the wall of the spore case is 



ruptured the elaters are liberated, 



and by their active motion assist in 



discharging the spores. 



In most of the true mosses the 



spore case opens by pushing off a 



lid at the apex, which exposes a 



delicate fringe of teeth covering the 



mouth of the urn-like case. These 



teeth bend in and out of the open 



spore case as they become moist or 



Fig. 123. A pod of wild hean 

 bursting, the two valves 

 violently twisting and dis- 

 charging the seeds.— After 

 Beal. 



