XX PREFACE. 



Cyclamen) are kept cool and moist by being laid on the 

 ground ; they thus mature more slowly, and are enabled 

 to grow to a larger size. In this simple action we prob- 

 ably see the first step to the further development of the 

 process, and to the capsules burying themselves beneath 

 the surface. In some cases the difference between the 

 subaerial and subterranean pods on the same plant and 

 both produced by cleistogamic flowers is extraordinary: 

 Mr. Meehan sent me three subterranean pods of Amphi- 

 carpwa monoica, each containing a single large seed ; and 

 my own plants produced several subaerial pods, each 

 containing from one to three small seeds. These latter 

 weighed on an average only tjV of the subterranean seeds ! 

 This difference, however, is not quite accurate, as the 

 coats of the subterranean pods adhered so firmly to the 

 seeds that they were not removed and were weighed 

 with them; but from their thinness and lightness they 

 could not have much affected the result. 



