ANGIOSI ERMS. 



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Niix-vomica, where, like the seed itself, it is broad and flat. This is clearly the 

 result of the endosperm which grows inwards from the periphery of the embryo-sac 

 leaving a free central space, which, as has already been mentioned, is very large 

 and filled with fluid in the case of the cocoa-nut. In these cases the endosperm 

 is therefore a hollow thick-walled sac, enclosing a roundish or flattened cavity. 



In a large number of families of Dicotyledons, the first leaves of the embryo, 

 the Cotyledons, grow, before the seeds are ripe, to so considerable a size that they 

 displace the endosperm which was previously present, and finally fill up the whole 

 space enclosed by the embryo-sac and the testa ; while the axial part of the embryo, 

 and the bud (plumule) that lies between the bases of the cotyledons, attain even 

 in these cases only inconsiderable dimensions. In these thick fleshy or foUaceous 

 cotyledons (which are then usually folded), the reserve of food-material accumulates, 

 consisting of protoplasmic substance or starch and fatty matter, which is in other 

 cases stored up in the endosperm, and is made use of during the development 

 of the seedling. This storing of the cotyledons with so large a quandty of 

 food-materials appears to take place by its transference from the endosperm; and 

 hence the diff"erence between those seeds which in the ripe condition contain no 

 endosperm ['exalbuminous'], and those which do contain it ['albuminous'] con- 

 sists essentially only in the fact that the food-material of the endosperm has passed 

 over in the former case before germination into the embryo ; while in the latter case 

 this only takes place during the process of germination. The presence or absence 

 of the endosperm in ripe seeds is more or less constant within large groups of 

 forms, and is therefore of value in classificadon. Of the better-known families, for 

 example, the Compositoe, Cucurbitaceae, Papilionaceae, Cupuliferae (the oak and beech), 

 &c., are destitute of endosperm. Sometimes also the embryo increases so greatly 

 in size that the endosperm appears as a thin skin surrounding it. 



We must now recur to the fertilised ovule in order to follow the formation 

 of the Embryo. In Angiosperms, as in Gymnosperms, the embryonic vesicle is not 

 immediately transformed into the embryo; the end which faces the micropyle 

 coalesces in its growth with the wall of the embryo-sac at its apical swelling; 

 its free end turned towards the base of the ovule then lengthens, and under- 

 goes one or more transverse divisions. The Pro-embryo, or Suspensor as it is more 

 frequently called, thus formed, usually remains short (Fig. 369, p. 511); somedmes, 

 as in Funkia, its basal cell swells up into a globular form (Fig. 368, p. 508) ; in 

 other cases (as, according to Hofmeister, in Loranthus) the embryonic vesicle 

 lengthens, and penetrates to the considerably enlarged base of the long tubular 

 embryo-sac, and there forms the embryonic vesicle within the endosperm. In those 

 Dicotyledons where the endosperm is formed only at certain lower parts of the 

 embryo-sac by division, a similar elongation of the embryonic vesicle is usual, 

 although not to so great an extent {e.g. Pedicularis, Catalpa, Labiatse). The apical 

 cell of the two- or more-celled pro-embryo which is turned towards the base of 

 the embryo- sac, and therefore also towards that of the ovule, is rounded off" into 

 a spherical form, a longitudinal or only slightly oblique division-wall first of all 

 makes its appearance in it, indicadng the commencement of the formation of the 

 embryo (see also Fig. 14, p. 17). As this grows by rapidly repeated divisions, a 

 spherical or ovoid mass of small-celled tissue is produced, on which the first foliar 



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