3M 



BOTANY OF THE LIVING PLANT 



the terminal cell of the pro-embryo. This occurs in the Dioscoreaceae and 

 Commelinaceae (Fig. 233), also in Zanichellia and others. There is reason 



Fig. 232. 



Successive stages of development of the embryo of Alistna, after Famintzin. 

 /, m, n, o, p, q represent successive cells of the pro-embryo, and the tissues derived 

 from them by division. 



to believe that the stem-tip in the embryo of the Monocotyledon was originally 

 terminal, as in the Dicotyledons, but that in most types it has been forced 

 to one side by the strong growth of the single cotyledon. If this were so the 

 A lisma-type would be a derivative, and secondary condition, and an apparent 



anomaly would thus be explained. For 

 among Vascular Plants the embryos of 

 the Alisma-ty-pe are the only exceptions 

 to an otherwise general rule ; which is, 

 that the apex of the shoot bears a con- 

 stant and close relation to the centre of 

 the distal tier of cells composing the 

 embryo. 



The very peculiar structure of the em- 

 bryo in Grasses has caused much discus- 

 sion (App. A, Fig. 503, p. 658). The 

 question has arisen whether the " scutel- 

 lum," which faces the endosperm, and 

 acts as a sucker from it, is or is not 

 the cotyledon. The view now held as 

 probable is that the cotyledon is highly 

 specialised. A basal part of it appears 

 as the scutellum, the distal part of it as the " cotylar sheath." The origin 

 of the plumule appears here also to be from the apex of the embryo. 



B 



Fig. 233. 



Embryos of Tamus. (After Solms-Laubach.) 

 A, younger; B, older. Si$»= suspensor. 

 H = hypophysis. E, body of "the embryo. 

 Here the embryology is more nearly of the 

 type of Capsella. 



