88 MOVING SEEDS. [chap. 



Other species possessing the same faculty of bury- 

 ing their seeds are Okenia hypogcea, several species 

 of CoTitmelyna, and of Amphicarpcea, Voandzeia sub- 

 terrafiea, Scrophularia arguta, &c. ; and it is very 

 remarkable that these species are by no means nearly 

 related, but belong to distinct families, namely, the 

 Cruciferm, Legmninoscz, Commelynacem, Violariecs, and 

 Scrap kulariacece. 



Moreover it is interesting that in L. amphicarpos, as 

 in Vicia amphicarpa and Cardamine chenopodifolia, the 

 subterranean pods differ from the usual and aerial form 

 in being shorter and containing fewer seeds. The reason 

 of this, is, I think, obvious. In the ordinary pods the 

 number of seeds of course increases the chance that 

 some will iind a suitable place. On the other hand 

 the subterranean ones are carefully sown, as it were, 

 by the plant itself Several seeds together would 

 only jostle one another, and it is therefore better that 

 one or two only should be produced. 



In the Erodiums, or Crane's Bills, the fruit is a 

 capsule which opens elastically, in some species 

 throwing the seeds to some little distance. The seeds 

 themselves are more or less spindle-shaped, hairy 

 and produced into a twisted hairy awn as shown in 

 Fig. 54, representing a seed of E. glaucophyllum. 

 The number of spiral turns in the awn depends upon 

 the amount of moisture ; and the seed may thus be 

 made into a very delicate hygrometer, for if it be 

 fixed in an upright position, the awn twists or un- 

 twists according to the degree of moisture, and its 

 extremity thus may be so arranged as to move up and 

 down like a needle on a register. It is also affected by 



