498 ItEV, GE0KGE HENSLOW ON A THEORETICAL 



Balanophora, Monotropa, Cuscuta, &c, and in some aquatic 

 genera, e. g. Zoster a > Hydrocharis, Vtricularia, and we may add 

 Hanunculus Fi carta. 



The authors give a useful epitome of the opinions of botanists 

 on the seed of Trapa, from Adanson, 1763, to Wittrock in 1887. 

 For example, Gaertner says : — " The cotyledons are unequal, the 

 one being very large and thick, the other minute, subrotund and 

 scale-like, adjacent to the base of the radicle. The plumule is 

 very minute, lying concealed within the small cotyledon/' He 

 adds, " It oscillates, like Nelumbo, between Monocotyledons and 

 Dicotyledons ; and since during germination only a single 

 cotyledon comes to light, strictly speaking it would be asso- 

 ciated with Monocotyledons." A. L. de Jussieu (1789) asks 

 whether the one-lobed seed did not show affinity with Naias ; 

 or rather, being bilobed, with perigynous stamens and corolla, a 

 four-fid calyx and four petals, it ought to be ascribed to the 

 genus Onagris. Hofmeister, like other writers, recognizes the 

 great inequality in the size of the cotyledons, the formation of 

 the plumule in a fissure at the base of the cotyledon and covered 

 by a scale, which he regards as the second cotyledon. He says 

 that there is no principal root in Trapa, as also is the case with 

 Ceratopliyllum, Naiadece, and OrcJiidece. His associating Cerato- 

 pJiyllum, a dicotyledonous aquatic genus, with Monocotyledons 

 is interesting as affording another corroborative instance of 

 an aquatic medium beiug correlated with an arrested primary 

 root. We shall see, however, that this feature is a general one. 



Ceratophyllum illustrates another point. We shall see that 

 the first leaves of the plumule of members of the NympJiaacea 

 are greatly degraded by arrest ; and in this genus the lower 

 leaves of the plumule have even assumed the character of coty- 

 ledons. The single cotyledon of Trapa is not lateral but 

 terminal as in monocotyledons ; and, except in the absence of 

 endosperm, which, however, is a characteristic feature generally 

 of aquatic monocotyledons, the authors observe that the develop- 

 ment of the embryo resembles that of typical monocotyledons. 



The association by these authors of Trapa natans with the 

 embryos of parasitic as well as with those of other aquatic mono- 

 cotyledons points to another and very potent cause of degene- 

 ration, which often produces very similar features in the ovules 

 and seeds and even a greater amount of degradation in the 

 vegetative system, as seen in the total absence of chlorophyll- 



