HOW PLANTS GROW. 227 



chain of cells gradually elongating, and forming the Suspe?isor, or 

 Fro-embryo ; the lower one developes by similar division and 

 growth into the Embryo itself. This increases by repeated divi- 

 sion, and soon begins to assume a more definite shape, to be seen 

 presently. One fact in passing. While the embryo is growing, 

 there are developed at the lower end of the embryo-sac by free 

 cell-formation a number of cells, filled with nourishing matter, 

 called Endosperm, or Albumen. On this the growing embryo feeds 

 by absorption. In some cases, similar cells are seen outside the 

 sac — i.e., in the nucleus of the ovule ; the nourishing matter is 

 then called Perisperm, from its situation. 



We must here glance at the " regions " of the growing embryo, 

 and see their relation to the parts of the plant as we know them 

 in its adult state. 



The Embryo now consists of three primary layers of cells, as 

 follows: — I. An outer layer, called Dermaiogen, or Epidermal 

 tissue, which is formed first. 2. A layer below this, called Feri- 

 blem, or Primary Cortical tissue. 3. Enclosed by these two is a 

 third, called Flerome, or Intermediate tissue ; this breaks up into 

 two layers almost directly : an outer one, called the Frocambium, 

 and a central part, the Fundamental tissue. Thus we get three 

 primary tissues, the innermost of which divides into two more, 

 making four in all. 



From these four are developed all the tissues of the adult 

 plant, which lie very much in a similar relation to one another 

 from circumference to centre, as do the embryonic tissues. 



From the Dermatogen comes the Epidermis, with its append- 

 ages — hairs, stings, scales, prickles, bristles, glands, and the like ; 

 from the Feriblem comes the Frimary Cortex, known as the bark, 

 with its bast-fibres, milk-vessels, and glandular cells ; from the Fro- 

 cambium come the Fibro-vascular bundles, as they are called, 

 which can be traced into the branches and leaves, and which 

 form the wood of our trees, and the harder, firmer parts of 

 the stem and leaves, including the wood-fibres, vascular cells, 

 true vessels, sieve-tubes, and bast-fibres; finally, from the 

 Fundamental tissue are formed the Fith and the Medullary 

 Rays, which radiate from the pith outwards between the fibro- 

 vascular bundles, and form the " silver grain " of wood. All these 



