Dr. Smith's Inguinj into the Structure of Seeds. 213 



position of the Cotyledons in all seeds, the oxygen gas must al- 

 ways be imbibed by their under side, that very same part which 

 in leaves gives out this kind of gas during the day, and probably 

 absorbs it during the night. It would have evinced a strange 

 contrariety in the constitutions of two organs otherwise so ana- 

 logous, I mean the leaves and cotyledons, if the upper surface 

 of the latter, while in the unexpanded seed, had been presented 

 to receive the oxygen gas. Where there is a separate Albumen, 

 without any perceptible Cotyledons, it is probable that the stalk 

 of the Embryo may answer the necessary purpose; just as the 

 steins of leafless plants must be presumed to perform the usual 

 chemical functions of leaves, though we cannot ascertain in 

 what direction the different airs are imbibed or discharged, there 

 being no decided upper or under surface in such stems, any more 

 than in ensiform leaves. Such, however, are rare exceptions, 

 which if not, as yet, found to throw any new light on the sub- 

 ject, certainly do not overturn any important part of the above 

 hypothesis. That some part, immediately connected with the 

 Embryo, must be stimulated in order to excite the germina- 

 tion of a seed, this phenomenon being dependent on the 

 vital principle, is evident. I conceive that, when present, 

 the Cotyledon or Cotyledons are themselves stimulated by 

 the oxygen gas, or rather by the heat which chemists in- 

 form us is produced by the absorption of that gas, so as 

 to set their fluids in motion, and thus to propel the young 

 root and rising Plumula. But when the Cotyledons are want- 

 ing, the Embryo may very well be conceived capable of suf- 

 ficient action to imbibe for itself the juices of a distinct Al- 

 bumen, already become milky and saccharine by the reception 

 of oxygen and moisture, by which merely chemical process, as 

 in barley, so considerable a degree of heat is evolved, as must 



very 



