STATE POMOLOGICAI, SOCIETY. 39 



tree. If we should cut a thin section from a leaf, a stem or 

 root and examine it with a microscope we would find that 

 instead of being solid it presents a honeycombed appearance. 

 We would at once see that the plant tissues are made up of 

 different individual units of various shapes and sizes. Further- 

 more, in each separate organ, the shape, size, structure and 

 arrangement of these units are modified to serve some special 

 purpose. For exami^le, in the leaf they have thin walls, are 

 more nearly rectangular, and are arranged with open spaces like 

 a loosely piled stone wall. In the stem of woody trees the dif- 

 ferent elements are arranged in a circle and many of them are 

 thick walled, very long and tapering with the ends over-lapping 

 and fitting tightly together, thus giving strength to the tree. 

 Others have lost their end walls and form tubes or vessels to 

 conduct liquids up through the stem to the leaves. These sepa- 

 rate units are called cells and each cell of a plant is more or less 

 dependent on other cells for its life and well being. 



The simplest form of a vegetable cell has a wall made up of a 

 substance known as cellulose. Chemically this is practically the 

 same as starch but in structure it is in reality quite different, 

 as will be seen when I tell you that the best filter paper used by 

 chemists is nearly pure cellulose. It absorbs water very readily 

 and readily allows water to pass through it. On the other hand, 

 when wet, as it always is in the active cells, it retards the passage 

 of air or gases unless in solution much the same way as we have 

 all seen a wet sheet enclose and retain bubbles of air when in a 

 wash tub. 



The cell wall may be variously modified as the tree grows 

 older, those of the trunk becoming very thick and woody. 

 Those of the bark receive deposits of cork and the cells finally 

 become minute, tight, thick-walled cork boxes, each containing 

 a little bubble of air and forming an admirable non-conductor 

 to protect the tissues below from extremes of temperature with- 

 out. Lining the inside wall of all living vegetable cells is a thin 

 layer of a semifluid, viscid substance called protoplasm and 

 imbedded in it or suspended in the interior of the cell by strands 

 of protoplasm is a body called the nucleus. The protoplasm is 

 the seat life in the cell and the nucleus probably controls the 

 vital activities of the protoplasm. The cell cavity within the 

 film of protoplasm is filled with the watery cell sap, and bubbles 



