OVMNOSPERMS. 499 



Strasburger states that each of these bodies is formed from an endosperm-cell 

 lying at the apex of the embryo-sac, which increases considerably in size and 

 produces the neck and central cell of the archegonium by division. According 

 to the same authority a small upper portion of the central cell beneath the neck 

 is even separated as the canal-cell. There is litde doubt that, as Strasburger asserts, 

 the whole of the central cell is to be considered as the oosphere, although Hofmeister 

 thought that a number of oospheres arose in it by free cell-formation^. After the 

 pollen-tube has penetrated the tissue of the nucellus and forced itself as far as the 

 archegonium (corpusculum), where its fertilising material is conveyed to the oosphere, 

 the Suspensor is formed by division of a cell which is developed in the lower part of 

 the oosphere. The cells of the suspensor are at first small, but the middle or upper 

 ones elongate very much, and, pushing the lower ones before them, penetrate into a 

 softened part of the endosperm. Sometimes the suspensors which are produced side 

 by side separate ; each bears at its apex a small-celled rudiment of an embryo. On 

 this account, and also because several archegonia are often fertilised in one endo- 

 sperm, the unripe seed contains several rudimentary embryos, of which, however, only 

 one usually increases greatly in size, the others withering away. 



During the development of the embryo, the endosperm becomes filled with 

 nutrient materials and increases greatly in size ; the embryo-sac which encloses it 

 grows at the same time, and finally entirely absorbs the surrounding tissue of 

 the nucellus ; the integument, or an inner layer of it, becomes developed into a 

 hard shell, while frequently (in naked seeds) its outer mass of tissue becomes 

 fleshy and pulpy and gives the seed the appearance of a drupaceous fruit {e. g. 

 Cjycas, Salisburia). The effect of fertilisation not unfrequently extends also to the 

 carpels or other parts of the flower, which grow considerably, forming fleshy or 

 woody coatings to the seeds, or cushions beneath them. 



The ripe Seed is always filled with the endosperm, in which the embryo lies 

 and is distinctly differentiated into stem, leaves, and root. It fills up an axial 

 cavity of the endosperm, is always straight, its radicle being turned towards 

 the micropyle, its plumule towards the base of the seed. The first leaves which 

 the embryonal stem produces stand in a whorl, consisting generally of two opposite, 

 but not unfrequently of three, four, six, nine, or more members. At the period of 

 germination the radicle first protrudes through the split testa ; the bud which is 

 formed between the Cotyledons or first leaves at the apex of the stem is forced out by- 

 their elongation, the cotyledons still remaining concealed in the seed, and remaining 

 in it until its food-materials have been completely consumed by the embryo. Some- 

 times they remain concealed there as organs which have become useless ; but in 

 Coniferae they are drawn out by the elongation of the embryonal stem and brought 

 above the surface of the ground, where they unfold as the first foliage-leaves. The 

 cotyledons of Coniferse become gr^en even within the seed in complete darkness, the 



vol. I. pp. 567 and 570). The structure of the neck of the archegonium was made out by Hofmeister, 

 who applied to it the term rosette (On the Higher Cryptogamia, p. 411). Archegonium and 

 corpusculum do not seem exactly synonymous, since the latter, properly speaking, is only equivalent 

 to the central cell of the former. Henfrey termed the central cells 'secondary embryo-sacs' 

 (Elementary Couri-e, 2nd edition, p. 608).] 



^ More will be said on this subject under Coniferae. 



K k 2 



