ANGIOSPERMS. 



5ii 



unconnected with one another (Fig. 370) ; as they increase in size these primary 

 endosperm-cells may at once fill up the sac, coming into contact with one another 

 laterally and meeting in the middle (as in Asclepiadese and Solanacese) ; or new 

 endosperm-cells may be again formed by free cell-formation within the parietal 

 layer of cells first formed, which have already multiplied by division. They form 

 an internal lining to the primary endosperm-cells until the whole space of the sac 

 is filled up ; if the sac increases greatly in size, as, for instance, in Ricinus and the 

 large-seeded Papilionaceae, the filling up with endosperm does not take place till 



Fig. ^f»).— Viola tricolor; A longitudinal section through the anatropous ovule after fertilisaticn, // tl-.e placenta, 

 ■w cushion on the raphe, a outer, b inner integument, / the pollen-tube which has entered the micropyle, e the embryo-sac 

 containing the embryo (to the left) and a number of young endosperm-cells ; /> and C tlie apical swelling of two embryo-sacs 

 e with the embryo eb attached to it ; the pro-embryo in A' is two-celled. 



later, and the centre of the sac is filled in the unripe seed with a clear vacuole-fluid. 

 In the embryo-sac of the cocoa-nut, which grows to an enormous size, this fluid — the 

 cocoa-nut-milk — remains until the seed is fully ripe, the tissue of the endosperm 

 forming a layer only some millimetres in thickness, which lines the inside of the 

 testa. The very narrow elongated embryo-sacs of plants with small seeds, as Pislia 

 and Arum, arc filled up by a single longitudinal row of cells formed by free cell- 

 formation. In a large number of dicotyledonous plants (as Loranthaceas, Oro- 



FlG. 370. — P'iola tricolor, posterior part of the embryo-sac, £• its cell-wall, 3" the cavity of the cell, A', A' young 

 endosperm-cells wliich have been produced in the protoplasm pr. 



banchcoe, Labiata?, Campanulacea?, &c.), with long narrow tubular embryo-sacs, 

 the space of the embryo-sac is first of all divided by two septa, further divisions 

 succeeding in all or some of the cells thus formed ; the tissue of the endosperm is 

 produced from these last cells, and in this case often fills up only certain parts 

 of the embryo-sac; or the sac is divided by a septum into two daughter- cells, the 

 upper of which contains the rudimentary embryo, and produces endosperm in 

 small quantities by free cell-formation {e.g. Nymphaea, Nuphar, Ceratophyllum, 

 Anthurium^). In a few families only the formation of endosperm is rudimentary, 

 and limited to the temporary appearance of a few free cells or nuclei, as in Tropie- 



* For further details of these processes desciibcd by Hofmeister, vide infra, under the character- 

 istics of Dicot\ledon3. 



