424 MOKFHOLOGY. 



racece amongst the Monocotyledons, and in the Ranunculacece, 

 Papaveracea, Umbelliferce amongst the Dicotyledons, &c. Even 

 where the embryo-sac is very narrow, such an endosperm is often 

 to be detected in the vicinity of the embryo, as, for instance, in the 

 Nymph&acece and the Hydropeltidece. Very rarely indeed, and, so far 

 as I yet know, only in the Cocoinece among the Palms, the process 

 of cell-formation, starting from the walls of the embryo-sac, forms 

 only a thicker or thinner lining to the cavity, while this is not 

 occupied by the embryo, which is relatively exceedingly small. 

 The cavity in this case still contains, even in the ripe seed, the 

 formative fluid (cytoblastema), together with cell-nuclei and some 

 free cells. This fluid is the so-called milk of the cocoa-nut. 



The ulterior development of the new cellular tissue varies much, 

 sometimes the walls are completely converted into cellulose, some- 

 times they remain in a condition which is at least very little removed 

 from gelatine (as in the species of Cassia), or form various inter- 

 mediate conditions between this, amyloid and cellulose, which in 

 the dry seed are commonly called horny. The cell-walls some- 

 times remain quite thin, sometimes they become porously thickened 

 in various ways : their contents are the usual contents of cells 

 assimilated vegetable matter, in which frequently some one con- 

 stituent particularly preponderates, as oil, starch, &c. Very rarely 

 crystals of oxalate of lime are found in the endosperm (as in Pothos 

 rubricaulis). 



As has been already remarked, the embryo-sac, in its formation, 

 sometimes displaces a greater and sometimes a smaller portion of 

 the nucleus. When a portion remains, two conditions may be 

 distinguished according to the form of the seed-bud. In nuclei 

 with straight axes the embryo-sac grows more or less through the 

 axis of the same, and it is then surrounded by the remaining por- 

 tion of the nucleus (as in Nymph&acece, HydropeltidecB, and Pipe- 

 racece) : on the other hand, where the axes of the nuclei are curved, 

 the embryo-sac only displaces that part of the nucleus correspond- 

 ing to the circumference of the seed-bud, and its persistent part is 

 embraced in annular form by the embryo-sac (as in the Portulacece, 

 Caryopliyllace.ee, &c.) This persistent part of the nucleus is termed 

 perisperm : it consists, so far as I know, only of perfectly developed, 

 thin-walled cells, the contents of which are amylaceous or watery, 

 or consist of the usual assimilated matter. 



In Canna alone the peculiarity exists that the nucleus is very 

 early displaced by the embryo-sac, but the substance of the chalaza 

 remains as perisperm. 



All these masses of cellular tissue are called in descriptive 

 botany, without regard to the manner of their origin, albumen. 



The study of development which arose with the intelligent Italian 

 Malpighi was soon lost in oblivion. Treviranus again revived it, but 

 did not arrive at the recognition of its profound importance as the prin- 

 ciple of the whole science. Robert Brown was the first to demonstrate 

 how, in all matters connected with plants, the history of development 



