i88i; 



on Fruits and Seeds. 



G23 



Fig. 



will fiiul 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 ono another, and it is 

 therefore better that one or two only should be pro- 

 duced. 



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. 20, representing a seed of E. glaucophjllum. 

 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 

 untwists 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 aficcted 

 by heat. Now if the awn were fixed instead of the 

 seed, it is obvious that during the process of untwist- 

 ing, the seed itself would be pressed downwards, 

 and, as M. Eoux has shown, this mechanism thus 

 serves actually to bury the seed. His observations 

 were made on an allied species, Erodium ciconium, 

 which he chose on account of its size. He found that 

 if a seed of this plant is laid on the ground, it 

 remains quiet as long as it is dry ; but as soon as it 

 is moistened — i. e. as soon as the earth becomes in a 

 condition to permit growth — the outer side of the 

 awn contracts, and the hairs surrounding the seed 

 commence to move outwards, the result of which is 

 gradually to raise the seed into an upright position with its point on 

 the soil. The awn then commences to unroll, and consequently to 

 elongate itself upwards, and it is obvious that as it is covered with 

 reversed hairs, it will probably press against some blade of grass or 

 other obstacle, which will prevent its moving up, and will therefore 

 tend to drive the seed into the ground. Iftlien the air becomes dryer, 

 the awn will again roll up, in which action M. Koux thought it would 

 tend to draw up the seed, but from the position of the hairs the 

 feathery awn can easily slip downwards, and would therefore not 

 affect the seed. When moistened once more, it would again force the 

 seed further downwards, and so on until the proper depth was obtained. 

 A species of Anemone {A. montana) again has essentially the same 

 arrangement, though belonging to a widely separated order. 



A still more remarkable instance is afforded by a beautiful South 

 European grass, Stipa j^cnnata (Fig. 21), the structure of which has 

 been described by Vaucher, and more recently, as well as more com- 

 pletely, by Frank Darwin. The actual seed is small, with a sharp 



Erodium 

 qlaucophijUuin. 

 (After Sweet) 



