Chap. II. EUDIMENTAEY COTYLEDONS. 97 



hand, with several other Cacteae, the hypocotyl is from 

 the first much enlarged, and both cotyledons are 

 almost or quite rudimentary. Thus with Cereus Land 

 heckii-two little triangular projections, representing the 

 cotyledons, are narrower than the hypocotyl, which is 

 pear-shaped, with the point downwards. In Rhipsalii 

 cassytha the cotyledons are represented by mere points 

 on the enlarged hypocotyl. In Echinocactus virideseens 

 the hypocotyl is globular, with two little prominences 

 on its summit. In Pilocereus Houlletii the hypocotyl, 

 much swollen in the upper part, is merely notched on 

 the summit ; and each side of the notch evidently repre- 

 sents a cotyledon. Stapelia sarpedon, a member of the 

 very distinct family of the Asclepiadeas, is fleshy like 

 a cactus ; and here again the upper part of the flattened 

 hypocotyl is much thickened and bears two minute coty- 

 ledons, which, measured internally, were only -15 inch 

 in length, and in breadth not equal to one-fourth of the 

 diameter of the hypocotyl in its narrow axis ; yet these 

 minute cotyledons are probably not quite useless, for 

 when the hypocotyl breaks through the ground in the 

 form of an arch, they are closed or pressed against one 

 another, and thus protect the plumule. They after- 

 wards open. 



From the several cases now given, which refer to 

 widely distinct plants, we may infer that there is some 

 close connection between the reduced size of one or 

 both cotyledons and the formation, by the enlargement 

 of the hypocotyl or of the radicle, of a so-called bulb. 

 But it may be asked, did the cotyledons first tend to 

 abort, or did a bulb first begin to be formed? As 

 all dicotyledons naturally produce two well-developed 

 cotyledons, whilst the thickness of the hypocotyl and 

 of the radicle differs much in different plants, it seems 

 probable that these latter organs first became from 



