442 PART III. THE CLASSIFICATION OF PLANTS. 



The following are noteworthy peculiarities in the morphology and physiology 

 of the suspensor. It is generally a filament consisting of a longer or shorter 

 single row of cylindrical cells, sharply defined from the rest of the embryo : in 

 some cases it consists of several such rows {e.g. Glaucium, Viciese) : in others 

 it is massive (see above), consisting of a number of cells covering the posterior 

 end of the embryo, and not sharply defined from it : sometimes it consists 

 of a single cell {e.g. Funkia) : in some plants {e.g. Viciese) the segments of 

 the suspensor are coenocytic. Rarely, it is differentiated at a relatively late 

 stage of embryogeny {e.g. Cytisus Laburnum^ and some other Leguminosao). Its 

 common function is, by its growth, to force the embryo into the nutritive tissue 

 of the seed, and it is usually attached by its upper end to the micropylar end 

 of the embryo-sac : but it is not unfrequently adapted, more particularly when 

 the embryo-sac contains little or no store of nutriment, as an organ of ab- 

 sorption. Thus in some Orchids {e.g. Anacamptis pyramidalis, Flatanthera 

 bifolia. Orchis latifoUa), the filamentous suspensor grows through the wall of the 

 embryo-sac, and out at the micropyle, reaching the wall of the ovary where it 

 buries itself in the tissue of the placenta, from the cells of which it absorbs 

 nutriment for the embryo attached to its other end in the embryo-sac. Again^ 

 in other Orchids (Phalffinopsis, Vanda), the primitive suspensorial cell divides 

 longitudinally into six cells which grow out into long filaments, both upwards 

 and downwards, enveloping the embryo but not leaving the ovule, which act as 

 absorbent organs. In Tropaeolum, the suspensor produces two lateral branches, 

 one of which bores through the wall of the ovule into the cavity of the ovary, 

 acting as an anchor for the embryo ; the other penetrates the wall of the ovule, 

 where it is in contact with the placenta, and, entering the placental tissue, acts 

 as an absorbent organ. In Gnetum the suspensor branches and bears an 

 embryo at the end of each branch. When the suspensor is massive, it is itself 

 a depository of nutrient substances for the use of the embryo. 



No suspensor is developed in the following plants : Pistia StratioUs, Listera 

 ovata, Epipactis palustris and latifolia, Cypripedium spectabile, among Mono- 

 cotyledons ; Corydalis cava, and certain Leguminous plants, such as the 

 Mimosese and some Hedysareje, among Dicotyledons ; Ginkgo, among Gymno- 

 sperms. 



In those plants which have no suspensor, the development of 

 the embryo from the oospore is simple. The oospore divides 

 by a transverse (basal) wall into two ; then by a longitudinal 

 wall into four; and then by a second longitudinal wall, at 

 right angles to both the preceding, into eight cells, octants of a 

 sphere : generally speaking, from the half of the oospore next 

 the micropyle the primary root is developed, from the other half 

 the growing-point of the primary stem and the (one or two) 

 primary leaves or cotyledons. The early stages of the embryogeny 

 are essentially the same in those plants in which, though a sus- 

 pensor is present, it does not contribute to the structure of the 

 embryo, though here it is the embryo-cell that divides into octants. 



