278 



BOTANY OF THE LIVING PLANT 



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

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



Successive stages of development of ttie embryo of Alis}na, after Faraintzin. 

 /, m, n, 0, p, (7 represent successive cells of the pro-embryo, and the tissues derived 

 from them bv 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-type would be a derivative, and secondary condition, and an apparent 



anomaly would thus be explained. For 

 among Vascular Plants the embryos of 

 the ^'i/is)na-type 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 

 embrj'o. 



The very peculiar structure of the 

 embryo in Grasses has caused mucli 

 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 highl)- speciahsed. 

 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 fronr the ape.x of the embryo. 



Fig. 220. 



Embryos of Tamus. (After Solms-Laubach.) 

 A, younger; B, older. SiSn^suspensor. 

 // =hypophysis. £, body of the embryo. 

 Here the embryology is more nearly of the 

 type of Capselh. 



