OF SANTALUM ALBUM. 73 



determine its conversion into a cell. The nucleus becomes perfectly defined, as separate 

 •from the surrounding protoplasm, just at the period of fertilization. At the same time 

 this surrounding protoplasm (contained in a ' primordial utricle ' lining the entire embryo- 

 sac, down to the septum of the bull) (Tab. XVII. fig. 6)), becomes more dense and granular, 

 sometimes exhibiting largish starch-granules. 



Little further change occurs at the apex of the embyro-sac for some time ; merely the 

 ceU-membrane enclosing the nucleus becomes thicker, and the cells assume a more elliptical 

 form. The next step is the formation of endosperm-cells from the protoplasm of the 

 embryo-sac. This takes place by segmentation, or free ceU-formation from the whole 

 abundant mucilaginous protoplasm, commencing always in the bulb, often advancing 

 from them before it proceeds up the tubular part of the embryo-sac, which at first presents 

 only a single row of ' primordial utricles ' (Tab. XVII. fig. 12) ; the latter then divide 

 perpendicularly (Tab. XVII. fig. 13), and the cells produced, appear to apply themselves 

 to the side-waUs and multiply for some time by free cell-formation in the centre 

 (Tab. XVII. fig. 15). Ultimately cell-dinsion occm-s, and the whole cavity of the swoUen 

 embryo-sac being filled up with ceUular tissue analogous in character to that of the 

 nucleus, — namely, composed of squarish cells with thin walls, filled with dense protoplasm, 

 containing increasing quantities of minute starch-granules, — the albumen of the end 

 becomes a distinct structm-e, on the sui-face of which aU trace of the originally bounding 

 embryo-sac is soon lost (Tab. XVII. fig. 16). 



The first change in the germinal vesicle is its elongation downwards into a cylindrical 

 form ; then cross septa appear (Tab. XVII. fig. IB g. Tab. XVIII. fig. 19 g) one after an- 

 other, so that it is converted into a short row of ceUs. The uppermost remains appressed 

 to the coagula in the apex of the embryo-sac, and does not appear to become developed 

 further ; forming a kind of suspensor. The lower cells midtiply greatly (Tab. XVIII. fig. 23) 

 and form an elongated, clavate ceUular body, the embryo, in which at first no trace of 

 regions can be detected, — only a greater density of the tissue and abundance of granular 

 contents at the cotyledonary (inferior) extremity (Tab. XVIII. figs. 22 & 24 g, fig. 25). 



The conditions of the walls of the ovary during these changes deserve some attention ; 

 the outer substance of the young fruit is formed of a firm layer of tolerably equal thick- 

 ness aU over, constituting what we may call the epicarp together Mith the mesocarp 

 (Tab. XVIII. figs. 27 &28 s). These define and correspond to the outward form of the 

 fruit. The portion immediately beneath the epidermis is composed of oblong cells with 

 then- longest dimension in the direction of the axis of the fruit ; these pass insensibly into 

 a denser layer of closely-packed polygonal cells with thick walls. These two regions are 

 coloured, while the endocarp is nearly colom-less (Tab. XVIII. figs. 27 & 28). The cells 

 of the mesocarp (well defined internally to the naked eye) appear, under the microscope, 

 to pass again insensibly into the soft endocarp (figs. 27 & 28 /•), composed of membranous, 

 globular, and polygonal cells, loosely packed, of much greater diameter, for the most part, 

 than those of the mesocarp. The endocarp (figs. 27 & 28 r) fills up the whole space between 

 the dark rind of the fi-uit (s) and the placenta (and o\'ules) {p,p), during the earlier 

 expansion of the ovary. TVTiere in contact with the embryo-sacs and placenta, it is of 

 denser texture and of dai-ker colom", having a definite, separable boundary. A perpendi- 



VOL. XXII. L 



