586 PHANEROGAMS. 



embryo-sacs, the space of the embryo-sac is first of all divided by two transverse 

 septa, further transverse divisions succeeding in all or some of the cells thus formed, 

 followed by longitudinal ones ; the tissue of the endosperm is thus formed, 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. Nymphcea^ 

 Nuphar, Ceraiophyllum, Anthurium'^). In a few families only the formation of endo- 

 sperm is rudimentary, and limited to the temporary appearance of a few free cells or 

 nuclei, as in TropcBolum, Trapa, Naiadeae, Alismaceae, Potamogetoneae, Orchideae ; 

 in Canna even this rudimentary production of endosperm appears to be suppressed. 



During the first formation of the endosperm, the embryo-sac usually increases in 

 size, and thus displaces the tissue of the nucellus which still to a certain extent 

 surrounds it ; only in a few cases is the nucellus still partially or entirely preserved ; 

 it becomes filled with food-materials, like the endosperm, and replaces this latter 

 as a reservoir of reserve-materials for the embryo. In most of the Scitamineae 

 {e.g. Canna), this tissue, the Perisperm, is very strongly developed, while the endosperm 

 is altogether wanting ; in the Piperaceae and in many of the Nymphaeaceae there is a 

 small endosperm in the ripe seed, lying in a hollow of the much larger perisperm. 



Fig. ^01.— Viola tricolor, posteriot part of the embryo-sac, e its cell-wall, 5 the cavity of the cell, A", A'young 

 endosperm-cells which have been produced in the protoplasm /r. 



While the endosperm surrounded by the embryo-sac increases in size, the Testa 

 is formed from the development of the integuments which accompanies that of the 

 endosperm; but in Crinum capense and some other Amaryllideae the growing endo- 

 sperm is stated by Hofmeister to burst the testa and even the wall of the ovary ; its 

 cells produce chlorophyll, and the tissue remains succulent and forms intercellular 

 spaces (which does not occur in other cases). In Ricinus a similar growth takes 

 place when the ripe seed germinates in moist earth, bursting the testa (according to 

 von Mohl); and the endosperm, previously ovoid and from 8 to lo mm. long, is 

 transformed into a flat broad sac 20 to 25 mm. in length, which surrounds the 

 growing cotyledons until they have absorbed all the food materials from it. 



In Monocotyledons and many Dicotyledons the embryo remains small and is 

 either enveloped by the endosperm or lies by its side (as in Grasses) ; the cells of 

 the endosperm, which are in close contact without intercellular spaces, become filled, 

 until the seed is ripe, with a protoplasmic substance and fatty matter or starch or 

 both, in which case they remain thin- walled ; it then appears as the mealy (full of 

 starch) or fatty portion of the ripe seed, the embryo being found by its side or 

 within it; but it is often horny in consequence of a considerable thickening of 

 its cell-walls which have the power of swelling {e.g. the Date and other Palms, 

 Umbelliferae, Coffea, &c.) If this thickening has taken place to a very great extent, 



* For further details on this point see the account of the Dicotyledons. 



