GROUPS OF PLANTS. 5 



This subject has an important bearing on the physiological 

 testing of drugs. Robert states that in determining the qualities 

 of a new chemical, preliminary experiments should be conducted 

 on lower plants and animals before trying it on man. Of the 

 plants which have been used in the testing of poisons the follow- 

 ing may be mentioned : Oscillaria, Spirulina, Nostoc, Zygnema, 

 Spirogyra, Saccharomyces, Mucor, Elodea, Lenina, Pistia, 

 Potamogeton, Myriophyllum, Ceratophyllum, Tradescantia, seed- 

 lings of grasses, lupine, bean, pea, corn, etc. 



Plant Organs. Depending upon the fact that the plant 

 requires nourishment for its growth and development and that 

 it has also to carry on the work of reproduction or propagation, 

 i.e., the production of new plants, we distinguish between 

 vegetative or nutritive organs and propagative or reproductive 

 organs. The vegetative organs, such as the root, stem and leaves 

 in higher plants, manufacture the food necessary for the life of 

 the plant, while certain other more or less specialized organs or 

 cells carry on the work of reproduction. 



In the lower plants, however, the whole structure is much 

 simpler, and in some instances a cell which performs the work 

 of a nutritive cell at one stage may become a reproductive cell 

 at another, or. as in the case of the unicellular Algae, all the 

 various functions of the plant may be carried on by a single cell. 



Generally speaking, there are two principal ways in which 

 plants are multiplied or reproduced : ( i ) By cell division or cell 

 fission, and (2) by the formation of special cells known as 

 SPORES. In cell division (Fig. 94) the nucleus and cytoplasm of 

 a cell divide to form two new cells or protoplasts, which become 

 distinct by the formation of a wall or cell-plate between the two 

 halves. All growth in plants is dependent upon this method, 

 and in growing parts the cells are said to be in a state of division. 

 Owing to the plasticity of the plant organism, detached portions 

 will often grow and give rise to new plants, as in the case of cut- 

 tings. Growth here as in the parent plant is accompanied by cell 

 division. In some of the lower Algse (Fig. 6) cell division is the 

 only method of propagation, and as only the ordinary vegetative or 

 nutritive cells of the plant are involved in the process it is some- 

 times spoken of as vegetative multiplication. 



