Fig. [26] offers an example of the square cells which usually form the bark of trees. This is a transverse section of cork, and perfectly exhibits the form of bark cells. The reader is very strongly advised to cut a delicate section of the bark of various trees, a matter very easily accomplished with the aid of a sharp razor and a steady hand.
Fig. [24] is a transverse section through one of the scales of a pine-cone, and is here given for the purpose of showing the numerous resin-filled cells which it displays. This may be compared with Fig. [16] of Plate I. Fig. [25] is a part of one of the “vittæ,” or oil reservoirs, from the fruit of the caraway, showing the cells containing the globules of caraway oil. This is rather a curious object, because the specimen from which it was taken was boiled in nitric acid, and yet retained some of the oil globules. Immediately above it may be seen (Fig. [23]) a transverse section of the beechnut, showing a cell with its layers of secondary deposit.
In the cuticle of the grasses and the mare’s-tails is deposited a large amount of pure flint. So plentiful is this substance, and so equally is it distributed, that it can be separated by heat or acids from the vegetable parts of the plant, and will still preserve the form of the original cuticle, with its cell-walls, stomata, and hairs perfectly well defined.
Fig. [7], Plate II., represents a piece of wheat chaff, or “bran,” that has been kept at a white heat for some time, and then mounted in Canada balsam. I prepared the specimen from which the drawing was made by laying the chaff on a piece of platinum, and holding it over the spirit-lamp. A good example of the silex or flint in wheat is often given by the remains of a straw fire, where the stems may be seen still retaining their tubular form but fused together into a hard glassy mass. It is this substance that cuts the fingers of those who handle the wild grasses too roughly, the edges of the blades being serrated with flinty teeth, just like the obsidian swords of the ancient Mexicans, or the shark’s-tooth falchion of the New Zealander.
These are but short and meagre accounts of a very few objects, but space will not permit of further elucidation, and the purpose of this little work is not to exhaust the subjects of which it treats, but to incite the reader to undertake investigation on his own account, and to make his task easier than if he had done it unaided.
CHAPTER V
Starch, its Growth and Properties—Surface Cells of Petals—Pollen and its Functions—Seeds.
The white substance so dear to the laundries under the name of starch is found in a vast variety of plants, being distributed more widely than most of the products which are found in the interior of vegetable cells.