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Commercial Gardening 



certain properties. They can absorb food materials, manufacture the food, 

 breathe, give off certain ingredients as waste products, reproduce them- 

 selves, and in two cases are possessed of motion, the 

 capability of which resides in the protoplasm itself 

 (fig. 2). The Protococcus can manufacture its own food 

 from raw materials, by reason of the presence of green 

 colouring matter under the influence of light. The 

 Yeast Plant must be supplied with malt, grapes (in 

 wine-making), or some other food already in an organ- 

 ized form. As the club-root fungus (Plasmodiophora 

 brassicai) is also colourless, it must have organized food, 

 and, as it feeds upon living plants, it is a parasite. 

 All of them absorb oxygen to give them energy, and 

 as it combines with some of their substance, carbon 

 dioxide is given off. The process is equivalent to 

 breathing or respiration, as in animals, and is abso- 

 lutely essential to all living things. 



2. STRUCTURE OF THE HIGHER 

 PLANTS 



Fig. 2. Protoplasm The Growth of a Cell. The three plants already 



SZSSiSSlio* considered consist of a single cell, varying chiefly in 

 of Arrows size during their lifetime. Other plants, in an as- 



cending scale of organization, consist of more or less 

 numerous cells united in a variety of ways to form the plant body, either 

 in the form of filaments, or flat plates of cells, as in freshwater or marine 

 algae. The larger seaweeds form a tissue resembling stem and leaves, but 

 a true stem and leaves are first met with in Mosses and Sphagnum. The 

 Ferns are still more . highly organized, by having true roots, stems, and 

 leaves. The flowering plants are the most highly organized, and gardeners 

 are chiefly concerned with them. The tiny Duckweeds, which cover still 

 ponds in summer, are flowering plants of very exceptional structure, for 

 they consist merely of a small mass of green cells, with one or more 

 root hairs from the under side. The smallest of all (Wolffia arrhiza) 

 has not even a root hair. The tallest tree and the smallest plant, 

 amongst flowering subjects, consist alike of an aggregation of cells, built 

 up in some definite form, according to the kind. 



A full knowledge of plants may be obtained by a study of proto- 

 plasm and its protective covering the cell wall together with their 

 behaviour when acted upon by light, heat, air, and moisture. A very 

 young cell may be taken from the leaf of an apple tree, when beginning 

 to unfold. It may be oval or nearly round. Under a high power of the 

 microscope the wall appears double, but each individual has its own 

 wall, and the other is the wall of the cells that abut on the one under 



