RUDIMENTARY COTYLrEDOXS. 



CHAP. II. 



this is exactly the kind of curvature which actually 

 occurs in these two plants, though to a much less 

 degree. Therefore we can hardly doubt that their 

 short hypocotyls have retained by inheritance a ten- 

 dency to curve themselves in the same manner as they 

 did at a former period, when this movement was highly 

 important to them for breaking through the ground, 

 though now rendered useless by the cotyledons being 

 hypogean. Rudimentary structures are in most cases 

 highly variable, and we might expect that rudimentary 

 or obsolete actions would be equally so ; and Sachs' 

 curvature varies extremely in amount, and sometimes 

 altogether fails. This is the sole instance known to 

 us of the inheritance, though in a feeble degree, of 

 movements which have become superfluous from 

 changes which the species has undergone. 



Fig. 60. 



Rudimentary Cotyledons. A few remarks on this 

 subject may be here interpolated. It is well known 



that some dicotyle- 

 donous plants produce 

 only a single cotyle- 

 don; for instance, cer- 

 tain species of Ranun- 

 culus, Corydalis, Chae- 

 rophyllum ; and we 

 will here endeavour to 

 show that the loss of 

 one or both cotyle- 

 dons is apparently due 



Citrus aurantium: two young seedlings: ^ o a store of nutri- 



c. larger cotyledon : c', smaller cotyle- , , . 1-1 



don ; h, thickened hypocotyl ; r, radicle, ment being laid Up m 



In A the epicotyl is still arched, in B it some other part, as in 



has become erect. , , f , 



the hypocotyl or one 

 of the two cotyledons, or one of the secondary radicles. 



