TRANSACTIONS OF SECTION K. 827 



that of the latter, both in shoot-system and root-system, is better adapted in 

 Dicotyledones in relation to water-supply. 



I specially differentiate the embryo-condition from the adult because in our 

 consideration of these higher plants we are apt to overlook the two distinct stages 

 into which their life is divided, and which call for altogether different adaptations. 

 There is, firstly, the life in the seed and in germination ; and secondly, there is 

 the life after germination. The conditions and the manner of life are not alike 

 in the two stages. In the tirst the plant is heterotrophic, in the second it is 

 autotrophic. The functions of the portion of the plant which lives the life 

 within the seed, and which bears the incipient epicotyl and primary root as small, 

 at times hardly developed, parts, are to absorb food, either before germination, as 

 in exalbuminous seeds, or during germination in albuminous seeds, to rupture the 

 seed-coat, and to place the plumular bud and the primary root in a satisfactory 

 position for their growth and subsequent elongation. The functions of the adult 

 may be summarised as the development and maintenance of a large assimilating 

 .ind absorbing area preparatory to reproduction. 



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 embryonal 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 suflicient evidence to show that the parts of the embryo are a reduction of 

 those of the adult. - 



The protocorm has, I believe, developed along different lines in the Dicotyledones 

 and Monocotyledones. This has been to the advantage of the former in the 

 provision that has been made for rapid as opposed to sluggish further develop- 

 ment. Confining ourselves to the general case, the axial portion of the proto- 

 corm of the Dicotyledon, the liypocotyl, 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 epicotylar leaves. In the IMono- 

 cotyledones the axial portion of the protocorm has usually no suctorial outgrowths. 

 Its apex and usually its base also are of limited growth. The plumular bud is a 

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

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



' The term has already been used for the embryo of Orchidea;, where the axis is 

 tuberous as is the structure to which the term has been given in Lycopodineas. But 

 tuberousness is not an essential for the designation corm. 



- I cannot pursue the subject here, nor discuss the view of the cotyledons as 

 either ancestral leaf- forms or arrested epicotylar leaves. The analogies with existing 

 Pteridophytes that are cited are not pertinent, for there is no evidence that Angio- 

 sperms have that ancestry, or indeed that their phylogeny was through forms with 

 free embryos. Nor is the fact of resemblance between cotjledons and epicotylar 

 leaves and the existence of transitions between them convincing. 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 internode, from which it is 

 intrinsically different as the frequent development upon it of hypocotylar buds 

 throughout its extent shows. 



^ In relation to this function it is noteworthy that the hypocotyl relatively 

 seldom in the exalbuminous seed of Dicotyledones becomes the reservoir of food- 

 material, whereas in Monocotyledones the axis of the embryo is the usual seat of 

 deposition. 



