STRUCTURE OF PLANTS. 



no internal stomach, and nitrogen is present in the seeds of almost all plants. More 

 recently, it has been averred that the'presence of a secretion, or product known as starch 

 ( Fi g- 4 )> would clearly establish the existence of vegetables ; but recent microscopic 

 researches have shown that starch is also met with in the lower classes of animals, 



Fig. 4. Section of a potato, showing the 

 grains of starch inclosed -within cells. 



Fig. 5. Varieties of DF.SMIDIJE.E, or SKA-WEEDS. 



A, clusters of Protococcus viridis. 



B, filament of Schizogonium murale. 



C, a similar filament, subdividing laterally at D. 



and in the brain and spinal cord of the higher animals, and even of man himself. Lastly, 

 certain of the Algce, or sea-weeds, as the Desmidiea and Diatomacea (Fig. 5), are still 

 claimed equally by the botanist and the zoologist. 



Thus simple as at first sight it might seem to state what a plant is as distinguished 

 from an animal, we find it impossible to distinguish the lowest plant from the lowest 

 animal ; and have therefore no alternative than to say that we cannot give an unim- 

 peachable definition of a plant. 



Definition of the Subject. We shall assume that our readers can recognise a 

 plant, although we cannot define it, and proceed to a description of those various parts 

 of which a plant is composed, and of the arrangement of plants into classes. These 

 two branches of the subject viz., structure and classification have a necessary 

 dependence upon each other ; for the idea of classification implies that certain members 

 have some properties or parts in common such, for instance, as the leaf or flower ; or 

 in other words, that their structure corresponds. Therefore a knowledge of structure 

 is essential to classification ; and before we describe the latter, we must indicate the 

 internal and external parts of which plants are composed. 



ANATOMY OR STRUCTURE OF PLANTS. 



Elementary Tissues. In proceeding to a consideration of the anatomy of 

 plants, it will be evident that, as plants in general have external organs, as leaves and 

 flowers, so must they have more minute parts of which these organs are composed. 

 These will correspond with the flesh and bones of the various parts of our body, and 

 are termed " elementary tissues." "We shall take them first in order, since they are 

 formed before the organs can be developed. They will also furnish us with drawings 

 of some of the most exquisitely-minute beauties of nature. 



Formative Fluid. But as the formation of a leaf, for example, implies the 

 previous existence of elementary tissues, so does the presence of an elementary tissue 

 imply the production of a material fluid, out of which the elementary structure was 

 formed. This latter is called the " formative fluid," or " organic mucus," or " cambium," 

 or " organizable matter" (all of which terms have the same original signification), and 

 is the sole source of production of every tissue foxmd in plants. It is, in this respect, 



