ANALYTICAL CLASS-BOOK OF BOTANrf. 



it will be remembered (30), all the vital forces are main- 

 tained. 



37. The Cellular System. — The whole substance 

 of all very young plants, the petals of flowers, the pulp 

 of fruits, and a large portion of roots, seeds and leaves, 

 are composed entirely of parenchyma. Also all the lower 

 orders of plants, or all lower than the Club-mosses, as 

 Mushrooms, Sea-weeds, Liverworts and Mosses, are 

 made up exclusively of cells, being composed of mem- 

 branous walls and the juices which they contain, or of 

 simple cellular tissue. This, on account of its tendency 

 to expand in a direction parallel with the plane of the 

 horizon, as may be seen in Lichens, Sea-weeds and leaves 

 generally, is collectively named the Horizontal System 

 of plants. The mechanical basis of parenchyma is mem- 

 brane, and the organic constituents of this are carbon, 

 hydrogen and oxygen. 



CHAPTEK IV. 



TEANSFOEMATIONS OF TnE CELLS. 



38. In the course of development, in almost all plants, 

 many of the cells undergo some very important changes. 

 These are chiefly caused by a thickening of the cell walls. 

 When this occurs, a secondary deposit is made on their 

 inner surface. This new layer, by evaporation of the 

 water it contains, passes into .the solid state, and thus 

 one layer withLa another may be formed, until the cavity 

 of the cell is nearly or quite filled up. Sometimes this 

 secondary deposit consists of organic material, solidified 

 by a portion of earthy matter, as in wood ; at other 

 times it seems to be composed almost entirely of inorganic 

 substances, as in the stone of fruits and the shell of 

 nuts, which are nothing but cellular tissue encrusted by 

 earthy matter. 



39. The gritty tissue of the Quince is composed of 

 cells formed in this manner, and so also is that of the 

 Pear, fig. 4, where it will be seen that the outline of the 

 cavity is very irregular — a circumstance which, in these 

 cases, often occurs. Even such soft pulpy fruits as the 

 Blueberry and Cranberry always have a portion of gritty 

 cells, which combine with their evanescent forms and 

 mellow juices the imperishable substance of the globe ; 

 and we know by their deposition of ashes in combustion 

 that this is true of flowers, for the same material that 



Cellular tissue, in what tribes and parts of the plant does it prevail ? What 

 system does it form ? Why so called ? Mechanical basis of parenchyma. Or* 

 ganic constituents. 



Subject of the Chapter. Secondary deposit. Where made? How formed? 

 Examples. Gritty tissue. Instances. Most important transformation, De- 



concretes in the rook and cements the mountain, is woven 

 into the exquisite petals of the Rose, and perhaps con- 

 tributes to give a mineral lustre to the almost transparent 

 whiteness of the Lily. 



40. But the most important of all these transfor- 

 mations is that by which Woody Fibre is developed in 

 the system. It is this which makes the framework of the 

 vegetable body, and corresponds with the bony skeleton 

 of the animal form. The proper woody tissue consists 

 of elongated cells, pointed at both ends, and overlapping 

 each other, so as to form continuous threads. The struc- 

 ture of the single tubes is best shown at fig. 18. The 

 upper part of the figure represents a transverse section, 

 or cut across the wooden tubes ; and the successive 

 layers, by which the tubes are nearly filled up, are well 

 shown, as they are also delineated by lines in the vertical 

 portion of the figure, where the white grooves in the 

 centre show the present extent of the calibre. But the 

 union of wood cells in compact bundles, as they occur in 

 the stem of trees, is best seen in fig. 2, at c c c. The 

 substance of wood is called Lignine. 



41. G-landular Woody Tissue. — The most impor- 

 tant modification of the proper woody tissue is that which 

 occurs in the great Cone-bearing family, known as the 

 Pine Tribe. The wood-cells of these trees are marked 

 with round spots or cavities, which are more or less fre- 

 quent throughout their tissue. At fig. 19 is seen a 

 single disc-bearing cell from the wood of the Fir tree. 

 These discs are not inclosed within the walls of a single 

 cell, but they occupy cavities in the opposite walls of 

 adjoining cells, which, exactly corresponding with each 

 other, unite and leave a hollow space between. Similar 

 discs are found in the Plane, and they are said to abound 

 in aromatic trees. In the Yew the discs are accom- 

 panied by a very delicate spiral fibre. Glandular cells, 

 in a petrified state, are sometimes seen in microscopic 

 studies of mineral coal, not only showing the vegetable 

 origin of such masses, but pointing to the Cone-bearing 

 tribe as their source. 



42. Bass Tissue is the Woody Fibre of the Bark, 

 and is composed of the longest cells in the vegetable 

 structure. It is this which gives to Flax, Hemp, and 

 all similar substances, their value in the manufacture of 

 cordage and woven fabrics. Fig. 15 represents a very 

 short bass-cell from the stem of Flax, lying across a cut 

 from a fibre of silk, fig. 16. The bass-tissue is formed in 

 the Liber, or inner bark, and hence is often called the 



scribe Woody Tissue, Wliat does it make ? With what correspond 1 L!g 

 nine. Glandular Woody Tissue. Describe discs. In what tribe chiefly 

 found? In what other trees? Discs in mineral coal — what ideas suggested? 

 Bass Tissue. What plants produce ? In what plants marked by ducts? 



