504 REV. GEOKGE HEN SLOW ON A THEORETICAL 



In concluding this part of the subject, I think the reader will 

 agree with me that there is at least enough presumptive evidence 

 to frame a theory that the monocotyledonous embryo has been 

 derived from a dicotyledonous one hy a suppression of one 

 cotyledon ; and that the cause of this suppression, as also, as we 

 shall see, that of the primary root together with various degrees 

 of degradation of the first leaves of the plumule, are due to the 

 degenerating effect of the aquatic medium in which the ancestral 

 endogens originally and primarily grew. 



It should always be remembered that similar effects often 

 follow in plants from various causes. Especially is this true in 

 the case where organs show signs of degeneracy. Thus, the 

 proembryonic state of the embryo may presumably be the result 

 of water in the cases mentioned in this paper; as, e.g., also in 

 Utricularia. It, however, also occurs in the Orchidece, which 

 are not aquatic, to which I have elsewhere alluded *. It is 

 found associated with other very degenerate conditions in many 

 parasites ; and it is also to be seen in saprophytes. 



Evidences furnished by the Order Nymph ^ace^e. — As 



the Nympliceacece are particularly remarkable for possessing 

 many points of agreement in structure with endogens, it will be 

 advisable to give somewhat in detail their peculiarities ; as these 

 will indicate in a collective manner the grounds for believing 

 generally that endogens acquired their peculiar features through 

 adaptations in a similar way to a watery medium. 



Stkuctural Eksemblaxces between Nymph^acejg asd 

 Endogens. — Much discussion was raised half a century ago upon 

 the anatomical structures of Nympliceacece, as to whether they 

 indicated an endogenous or exogenous position for this order. 

 The final decision was based upon the dicotyledonous embryo, 

 though it was recognized that they possessed several points of 

 structure showing similarity with endogens. It did not, however, 

 appear to have occurred to the observers that these very points 

 of supposed affinity with endogens were simply similar results 

 of adaptation to a watery medium. It is in the method of germi- 

 nation, the structure of the roots and rhizomes, and the develop- 

 ment of the foliage where the resemblances will be found f. 



* 'Origin of Floral Structures/ &c. p. 280. 



t For a full discussion up to the date of the work, see * Flora Indica/ by 

 Drs. Hooker and Thomson, vol. i. p. 233 (1855). 



