OKI GIN OF ENDOGENS FKOM EXOGENS. 505 



Germination. — The embryo has two thick cotyledons, which 

 remain within the seed-coat, and in the case of Nelumbium with 

 the radicle as well*. The radicle of other genera of this order 

 protrudes and develops a filiform primary root, or it is alto- 

 gether arrested (Huoker and Thomson). The plumule ascends 

 from between the cotyledons and gives off strictly opposite 

 leaves in a plane at right angles to that of the cotyledons. Of 

 these two, one has a vaginate petiole : this sheathing insertion of 

 the leaf, as pointed out, is another feature eminently charac- 

 teristic of aquatic plants whether they belong to exogens or 

 endogens. The other leaf is reduced to a mere filiform or 

 subulate petiole, and has no rootlets. It would seem that the 

 arrest has not aftected the cotyledons in this case ; but it has 

 influenced the first-formed leaves. In the cases of Trapa natans 

 and Ranunculus Ficaria, &c, as already mentioned, it has 

 reduced the two cotyledons to one only, or, still further, to the 

 proembryonic state. 



If the arrest of one cotyledon be due to an aquatic medium, it 

 must take place while the embryo is developing within the 

 embryo-sac. It has often been observed that while terrestrial 

 endogenous plants have their seeds supplied with endosperm, 

 those of endogenous aquatic plants and orchids are generally 

 devoid of it. This may perhaps be correlated with a similar arrest 

 having affected the embryo simultaneously. Thus " Herr F. 

 Hegelmaier describes several abnormal embryos of Nupliar 

 luteum in which the two cotyledons are more or less completely 

 united into a sheath, split only on one side; but the two halves 

 (corresponding to the two cotyledons) have been developed very 

 unequally, one of them being usually several times as long as 

 the other "f. 



Although members of the Nymphaacece are usually regarded 

 as dicotyledonous, we have here an important and independent 

 witness to the gradual arrest of one cotyledon. 



Arrest of primary Boot. — The next peculiarity of germination 

 is the tendency to, or complete arrest of the primary or axial 



" Etudes anatoniiques et organogeniques sur la Victoria rcyia, et anatomie 

 compared du Jselumbhtm, du Nuphar, et de la Victoria" par M. A. Trecul. 

 Ann. Sci. Nat, Bot. 4 ite. i. p. 145. 



t Extract from Jo urn. Boy. Micr. Soc. 1892, p. 387 ; a notice of Herr Hegel- 

 maier s paper, Jahr. Heft. Ver. vaterl. Naturk. Wiirttemberg, 1890, p. 88. See 

 Bot. Centralbl. xlix. (1892) p. 216. 



