MARKET DISEASES OF VEGETABLES. 



INTRODUCTION. 



THE NORMAL PLANT. 

 Plants and Plant Parts Are Living. 



T VEGETABLES and fruits are plants or plant parts and 

 V are alive. Few people realize that a potato, an onion, 

 an apple, or other fruit or vegetable is alive and is therefore 

 subject to injury, disease, and death. Failure to realize this 

 fact is responsible for much of the loss in the handling of 

 fruits and vegetables. 



The Structure of Plants. 



Our agricultural plants are composed of members or 

 organs, such as the root, stem, leaf, flower, and fruit. These 

 organs in turn are composed of tissues, the stem, for 

 example, usually being composed of pith, ring, and bark 

 tissue. Tissues, finally, are made up of cells, which are 

 microscopic in size. 



Plant tissues often are classified according to their func- 

 tions. There are, for example, the protective tissues, the 

 supporting tissues, the conductive tissues, the food-making 

 tissues, and the storage tissues. 



The Plant Cell and Tissues. 



The cell is the unit of composition, structure, and function 

 of all plants. It is composed of the living substance proto- 

 plasm, together with its products and inclusions. One of 

 the products of the jelly-like protoplasm is the rigid cell 

 wall in which it encases itself and which gives shape and 

 rigidity to the cell and to the tissues. Tissues and cell walls 

 often remain intact long after the protoplasm has died. In 

 some diseases, the cementing substance which holds adjoin- 

 ing cells together is dissolved out, and disintegration of the 

 tissue results. In other cases the cell walls are punctured 

 and the protoplasm is killed. Chemical analysis of plant 

 tissues, which are, of course, composed of cells, yields prin- 

 cipally water, proteins, carbohydrates, fats, and salts. Water 

 is by far the most abundant single constituent, most plant 

 tissues containing 70-75 per cent water. 



The structure of plant tissues is roughly comparable to 

 that of honeycomb except that the cells of plant tissues are 

 not as closely packed as those of honeycomb. There are 

 spaces between plant cells, called intercellular spaces, which 

 are most marked in leafy tissues. These constitute the ven- 

 tilation system of the plant, and through them the cells are 

 in communication with the air. 



The epidermis or outermost protective layer of cells of 

 leaves and young stems and roots has many minute open- 

 ings or breathing pores, the stomata. Through these, water 



