34 THE VEGETABLE KINGDOM. 



secondary matter inside the cell-wall. Always remembering 

 that a young cell is a simple sac of a single membrane, 

 which, containing a certain fluid, is capable of secreting 

 various substances, curiously separated from, or combined 

 with, the various gases and inorganic matter winch form 

 the soil in which it grows. These secretions are used for 

 strengthening the cell-walls as the young plant springs 

 upward ; therefore, if the deposit inside the cell is uneven, 

 it causes marks on the cell-wall; if the cell grows faster 

 than the supply of deposit, the markings are spiral or 

 arched, or waved, or dotted ; and these are best observed 

 by comparing different cells from fresh plants. The anther 

 of the vegetable marrow, if peeled and then examined with 

 a drop of water, will give beautiful cells of arched fibre. 

 But, to continue with this slide, these pits are at first only 

 dots in the secondary deposit; then as the cell thickens 

 these pits deepen, the primary membrane breaks, and they 

 become channels from cell to cell, as you may see in a 

 section of vegetable ivory, where you perceive radiations 

 from each cell, which are, in fact, these deep pits, and in a 

 vertical section would look like the pitted cells of Fir, or 

 Clematis, or Lime-wood, or Laurus sassafras, and many 

 others. 



VEGETABLE IVORY. 



Vegetable ivory is the seed of a palm called PJiytelepTias 

 macrocarpa, and is composed of a large round mass of bony 

 albumen, in which a small embryo is imbedded. Slices of 

 this ivory-like albumen, placed under the microscope, 

 affords very beautiful examples of these, thickened cells. 



FOSSIL CONIFEROUS WOOD. 



Fossil coniferous wood, which is wood converted into 

 lignite, or a kind of coal, when the vegetable matter is 

 almost entirely removed and replaced by silex (flint), pre- 

 serving all the peculiarities of structure. This fossil wood, 

 from Tasmania, will show the pitted ducts, which prove it 

 to be one of the Coniferse, or family of firs. 



Always add to your collection sections of 



