XIV INTBODUOTORT LESSONS. 



SECTION 2.— THE STRUCTURE OF PLANTS. 



Stems. While awaiting the development of germs in your experi- 

 mental garden, you can study plants which have already reached maturity 

 in wild gardens. Go out atid dig up the first plant — not too large — that 

 you find in blossom. I will su'ppose that you have found the very com- 

 mon Filaria (also called Pin-clover; and children call the curious seeds 

 with twisted tails, clocks). Its parts are Roots, Stem, Leaves, and Flowers. 

 (Some time, if you continue studying Botany, it will be proved to you 

 that flowers are forms of stems, or stem-branches.) 



" Crush the stem. It is made up of stringy fibers and a soft sub- 

 stance filled with juice. The former is generally called Fibrous I'issue 

 or Wood ; the latter. Cellular Tissue. The lower part of the stem and 

 the upper part of the root — the older portions of the plant — contain 

 more wood than the branches and the rootlets, while the leaves have only 

 net-4ike skeletons of wpod. It would be interesting to study these tissues 

 with the aid of a microscope, and thus become acquainted with the inner- 

 most structure of plants; but for the present it will be sufficient if you 

 can distinguish, in a general way, wood from cellular tissue. 



Cut. the stem squarely across near the upper end, and from one 

 piece take a thin slice. Stick this on a pin and hold it up to the light. 

 It is nearly transparent, except a green ring of skin outside and a ring 

 of white dots inside. The latter are cut ends of woody fibers which run 

 lengthwise of the stem. Make a similar section of the lower part of the 

 stem and you will find a continuous ring in place of the dots, showing 

 that in the older part the fibers have become so numerous as to form a 

 hollow cylinder of wood. The inclosed cellular tissue is called the Pith. 

 Exogens and Endogens. If the stem lives year after yesiV there will 

 be added successive layers of wood outside of the first one. Such stems 

 are woody, and if they grow many years become Bushes, Shrubs, or Trees. 

 Plants that grow in this way are called Exogens. Examine Asparagus, 

 Soap-root, Iris, or any Lily and you will find the wood fibers scattered 

 irregularly through the stems. These plants are Endogeiis. All our native 



