THE EMBRYO 209 



The same general idea has been expressed by Balfour, 80 as 

 the following quotations show : 



" We ought, I think, to look upon the embryo as a protocorm of 

 embryonic tissue adapted to a seed-life. Under the influence of its 

 heterotrophic nutrition and seed-environment it may develop organs 

 not represented in the adult plant as we see in, for instance, the embry- 

 onal intraovular and extraovular haustoria it often possesses. There 

 is no reason to assume that there must be homologies between the 

 protocorm and the adult outside an axial part with its polarity. There 

 may be homologous organs ; but neither in ontogeny nor in phylogeny 

 is there sufficient evidence to show that the parts of the embryo are a 

 reduction of those of the adult." 



"That the cotyledons, primarily suctorial organs, should change 

 their function and become leaf-like under the new conditions after 

 germination is no more peculiar than that the hypocotyl should take 

 the form of an epicotylar intemode, from which it is intrinsically 

 different as the frequent development upon it of hypocotylar buds 

 throughout its extent shows." 



"The protocorm has, I believe, developed along different lines in 

 the Dicotyledons and Monocotyledons. This has been to the advan- 

 tage of the former in the provision that has been made for rapid as 

 opposed to sluggish further development. Confining ourselves to the 

 general case, the axial portion of the protocorm of the Dicotyledon, 

 the hypocotyl, bears a pair of lateral outgrowths, the cotyledons, and 

 terminates in the plumular bud and in the primary root respectively. 

 The cotyledons are its suctorial organs, and the hypocotyl does the 

 work of rupturing the seed and placing the plumular bud and root by 

 a rapid elongation which commonly brings the plumular bud above 

 ground, protected, it may be, by the cotyledons. These latter may 

 then become the first assimilating organs unlike or like to the epico- 

 tylar leaves. In the Monocotyledons the axial portion of the proto- 

 corm has usually no suctorial outgrowths. Its apex and usually its 

 base also are of limited growth. The plumular bud is a lateral devel- 

 opment, and the primary root often an internal one. The suctorial 

 function is performed by the apex of the protocorm, termed here also 

 the cotyledon." 



"I use the term purely as an objective designation, and in the 

 original meaning of the suctorial organ in the embryo. This terminal 

 cotyledon in the Monocotyledons is not a leaf nor the homologue of 

 the lateral cotyledons in the Dicotyledons." 



An explanation of the terminal cotyledon of Monocotyledons 

 has been suggested by Miss Sargant s9 in her study of the seed- 

 lings of Liliaeeae. In AnemarrKena she finds the cotyledon 



