OX Till . i?.i T GTUR:E OF SEEDS. 363 



gree of heat is evolved, as must very powerfully exGite the 

 vital principle of the budding vegetable. In the few cases 

 where one or more cotyledons and a distinct albumen are to- 

 gether present, it does not seem necessary, that the gas 

 should act through the former upon the albumen, the two 

 organs being but little connected, and its operation on the 

 latter being independent of all vital or organic laws; but 

 either the gas itself, or the heat produced, may very well so 

 stimulate the vital principle of the cotyledons, as to propel 

 their fluids into the embryo, and assist germination. This 

 opinion is the more probable, as these Uuids must bo sup- 

 posed more truly of the nature of sap, and more immedi- 

 ately fit /or the use of the infant plant, than the liquor of 

 the albumen. However this may be, the existence of a co- 

 tyledon or cotyledons, together with a separate albumen, 

 in seeds, seems to me so unusual, as not to occasion much 

 difficulty, and I would define a cotyledon to be a vital or- Definitions of 

 gan, capable, as such, of being stimulated by oxigen, heat, th e cotyledon. 

 or both, for the propulsion of its contents ; while such an 

 albumen is merely a repository of nutritious vegetable mat- 

 ter, subject to the laws of chemistry alone, and only pas- 

 sively resigning those contents to the absorbing powers of 

 the embryo, to which it is attached. 



I must now, under the impression of what has just been. Arrangement 

 advanced, return to the arrangement of plants by their co- j^ t ^ nt ^ 

 tyledons. ledons. 



Plants in general are dicotyledonous, having a pair of these Those with 

 organs, which commonly rise out of the ground ; but if they tw0 or more * 

 do not, it appears;, from the consideration of the legumi- 

 nous tribe, that such a difference could scarcely serve for a 

 generic distinction, much less for that of a class or order. 

 It also appears, that, if the number of cotyledons exceeds 

 two, as in pinus and a fvw other instances, the difference is 

 of little or no use for systematical purposes, and of no 

 physiological importance whatever. The cotyledons of pi- 

 nus all present their backs to receive the oxigen. 



Some plants appear to bo really furnished with one simple Morncctyl©. 

 cotyledon, aszamia, and according to Gaertner's figures and 

 descriptions, tlie true scitaminew, as amomum (ids zingiber), 

 (ilpiiiid) &c 3 while canna geema to have no potykdou, but * 



only 



