20 STEMS. 



16. The stem grows in an opposite direction to the root, and 

 seeks the air and light ; in general, it rises vertically above the 

 soil, and serves to support the leaves, flowers, and fruit. 



17. Generally this part of a vegetable is very apparent and 

 easily recognised ; sometimes it is simple, at others branching, 

 and when it is simple below, and branching in its superior part, 

 the first part is called the trunk, and to the second we give the 

 name of branches. 



18. All vascular plants are provided with a stem, but some- 

 times it is so short and so enveloped in leaves, or so completely 

 hidden in the ground, that it seems not to exist ; vegetables thus 

 formed, are named a'caulous plants (from the Greek, a, without, 

 and kavlos, stem or stalk) ; but this absence of the stem is only in 

 appearance. 



19. Thus, in tulip and other bulbs, there exists 

 amidst the leaves in form of scales, of which the 

 greater part of these bodies is composed, a 

 tissue which separates these appendages from 

 the roots, and which constitutes a true stem 

 (Jig. 11); only, instead of being elongated and 

 cylindrical, as is ordinarily the case, it is gene- 

 rally globular and flattened above, an arrange- 

 ment which has procured for it the name of 



cormus or plateau. Fi &- H- BULB. 



20. Subterraneous or rhizome stems have the appearance of 

 roots, but are distinguished from them by their structure and 

 several other characters ; their tissue becomes green by the ac- 

 tion of light, which is never the case in true roots, and, under the 

 influence of moisture, branches spring up covered with leaves, 

 but radicles never grow from them. Sometimes these subterra- 

 neous stems bear, here and there, irregular tubercles. 



21. The stem of a plant assumes numerous and very different 

 appearances in different plants. 



Explanation of Fig. 11. A bulb or onion, showing the roots (o) ; the 

 cormus, or plateau, or representative of the stem (ft) ; and the leaves or 

 scales (c) ; Cormus (from the Greek Arormos, a stem), a rhizome, or subter- 

 raneous stem. 



16. In what direction does the stem grow ? What is the use of the 

 stem? 



17. What is meant by trunk and by branches ? 



18. Are all plants provided with a stem? 



19. What is a cormus ? 



20. How are subterraneous stems distinguished from roots ? What is 

 the effect of light on the colour of plants ? 



21. Is the form of the stem in all parts the same ? What are the forms ? 

 What is a scape ? 



. V " ' 



