PHYTOGENESIS. _.;7 



In the further progress of organization (in which process the 

 gum is always the last, immediately preceding fluid), a quantity 

 of exceedingly minute granules appear in it, most of which, 

 on account of their minuteness, look like mere black points. 

 Iodine then seems to colour the fluid a somewhat darker 

 yellow. The granules, however, when their size is sufficiently 

 large to render their colour perceptible, become of a dark 

 brownish-yellow under its influence. 



It is in this mass that organization always takes place, and 

 the youngest structures are composed of another distinct, per- 

 fectly transparent substance, which presents an homogeneous 

 colourless mass when subjected to pressure; when dried it 

 imbibes water and swells; it is not at all affected by tincture 

 of iodine, nor does it ever imbibe it ; after pressure it appears 

 as colourless as before, and is so completely transparent as to 

 be altogether invisible when not surrounded by coloured or 

 opaque bodies. This substance frequently occurs in plants (for 

 example, in great quantity, together with a little starch, in 

 peculiar large cells in the tubers of Orchis) ; for brevity's sake 

 I shall call it vegetable gelatine ; and am inclined to class 

 under this head, as mere slight modifications, pectine, the basis 

 of gum tragacanth, and many of those substances which are 

 usually enumerated under the term vegetable mucus. 



It is this gelatine which is ultimately converted by new 

 chemical changes into the actual cellular membrane, or struc- 

 tures which consist of it in a thickened state, and into the 

 material of vegetable fibre. 



I now pass on to our subject itself. There are two situa- 

 tions in the plant in which the formation of new organization 

 may be observed most easily and clearly, in consequence of 

 there being cavities closed by a simple membrane, viz. in the 

 large cell, which subsequently contains the albumen of the 

 seed, the embryonal sac, and in the extremity of the pollen- 

 tube, from which the embryo itself is developed. The em- 

 bryonal sac never contains starch originally, but probably, in 

 most instances, the saccharine solution (which gives the Bweet 

 taste to unripe pod-fruits and the Cerealia), or gum. 



The pollen, on the contrary, always contains starch, or the 

 above-mentioned granulous mucus representing it, as an essen- 

 tial constituent part. The so-called vegetable spermatozoa 



