ENDOSPERM. 763 



as often occurs, the endosperm presents the appearance of a number of transverse 

 walls dividing its cavity into chambers ; if, on the contrary, the embryo-sac is very 

 large, it may happen that the endosperm commences to form on the wall but 

 never fills up the whole of the cavity. This is conspicuously the case in the 

 Coco-nut, and is not rare to a slighter extent in other large-seeded plants : the 

 hard shell of the Coco-nut is clothed internally by the wall of the embryo-sac, and 

 we have here, therefore, an instance of a cell which attains a volume of 500 c. cm. or 

 more. The development of endosperm in the Coco-nut however proceeds only so far 

 as to form a layer of tissue 4-5 mm. thick at the circumference of this enormous 

 embryo-sac, in which the relatively tiny embryo lies: the whole of the remaining 

 cavity is filled with the watery cell-sap of the embryo-sac, known by the name of the 

 milk of the Coco-nut, and employed as a drink. In many other cases also the 

 embryo-sacs of- the Angiosperms are distinguished by their large size (as single 

 cells) immediately after fertilisation and subsequently : on cutting a half-ripe Bean it 

 appears as a vesicle filled with water. In like manner in the case of the Walnut, before 

 the shell of the nut becomes hardened, the large cavity which it surrounds is found to 

 be filled with watery fluid. In these and many other cases the cavity described is 

 the hollow of the embryo-sac, which subsequently becomes wholly or partly filled with 

 endosperm-tissue. 



The endosperm of ' the flowering-plants is distinguished from that of the 

 Gymnosperms, as is clear from what has been said above, from the fact that it 

 only arises after fertilisation. It resembles it, however, in that when the ovule ripens 

 into the seed it becomes filled with products of assimilation (proteids and starch or 

 fat) the at first extremely delicate cell-walls of the endosperm often undergoing 

 enormous thickening, so that the endosperm at last forms a very hard thick mass. 

 Such is the case for example in Coffee ; the so-called CofTee-bean, as it comes into 

 the market, being the horny hard endosperm. In the same way a Date-stone consists 

 entirely of very thick-walled endosperm-tissue (cf. p. 344). One of the most remark- 

 able examples in this connection is afforded by the large seeds of Phyfelepkas, a 

 tropical palmaceous plant, which on account of their enormous hardness and solidity 

 are worked by turners as vegetable ivory : the whole of the hard mass is thick-walled 

 endosperm, in which the small embryo lies at one point of the periphery, and 

 when it germinates it dissolves and absorbs the whole of this hard mass. To 

 remind the reader of but one more example, well-known to all, it may be stated 

 that the flour-yielding substance of our cereals is the endosperm in the embryo- 

 sac of these seeds, in this case consisting of very thin-walled large cells contain- 

 ing proteids and starch. 



There are both among the Monocotyledons (Orchidacese) and among the 

 Dicotyledons various families in which the formation of endosperm is either extremely 

 scanty or entirely suppressed. Such cases, however, must not be confused with 

 those where no endosperm is to be found in the ripe seed owing to its having been 

 absorbed by the embryo during the development of the seed. This is the case 

 particularly often among Dicotyledons: the kernel of such fruits as Cherries 

 and Almonds, Apples, and the Walnut and Hazel-nut, Acorns and Beech-nuts, 

 the seeds of the Sun-flower and of all Compositae, the seeds of Gourds and 

 Cucumbers, Peas, Lentils, Beans, etc. contain in the ripe state no endosperm 



