278 



BOTANY OF THE LIVING PLANT 



Commelinaceae (Fig, 220), also in Zanichellia and others. There is reason 

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



Fig. 219. 



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

 Z, m, n, 0, p, q represent successive cells of the pro-embryo, and the tissues derived 

 from them i)y division. 



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 

 Alisma-ty^Q 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 the 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 

 embr^^o. 



The very peculiar structure of the 

 embryo in Grasses has caused much 

 discussion. The question has arisen 

 whether or not the " scutellum," which 

 faces the endosperm, and acts as a 

 sucker from it, is or is not the cotyle- 

 don. 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. 



Fig. 220. 



Embryos of Tamus. (After Solms-Laubach.) 

 A, younger; B, older. SiS2=suspensor. 

 if=hypophysis. E, body of the embryo. 

 Here the embryology is more nearly of the 

 type of Capsella. 



