120 THE PLANT WORLD. 



II. The root is used to take the nourishment from the soil in the 

 form of water and chemical elements. The stem is used in most 

 plants as a medium of support and for carrying the food from the 

 roots. The leaves are the organs of respiration, photosynthesis, and 

 transpiration. 



HI. The petioles are very often lengthened at the base so as the 

 lower leaves may not be shaded by the upper ones; but each may have 

 all the light necessary for light relation. 



IV. In transpiration the leaves give off moisture and in respira- 

 tion the leaves take in oxygen and give off carbon dioxide the same as 

 animals do. 



V. The mesophyll is protected by the epidermal skin on the out 

 side of the leaf. In the upper portion of the leaf the cells are raised 

 on edge making a palisade tissue and also protecting the mesophyll. 

 When water is scarce and the heat and light very intense the palisade 

 tissue is often raised all over the leaf. 



VI. The three types of stems are those bearing foliage leaves, 

 those bearing scaly leaves, and those bearing floral leaves. An illus- 

 ti-ation of the first type is the maple tree, an illustration of the second 

 type is the cactus, and an illustration of the third type is the butter- 



CU}). 



VII. In a two year old stem-dicotyledon, there are four different 

 divisions. In the center is the pith, about this is the vascular tissue 

 with two rings indicating the number of seasons which the plant has 

 been growing, next is the cortex or a green fibry skin under the epi- 

 dermis which follows and is on the outside. 



VIII. Plants ward off enemies by six different means. These are 

 (1) by hairs, (2) by glandular secretion (3) by isolation, (4) by latex, 

 (5) by protective forms, and (6) by protective closure. 



IX. Velamen is the mossy or moss-like substance which grows on 

 the roots of air plants. 



X. The seed of the milkweed is a plumed seed. The seed of the 

 basswood is a winged seed. The beggar's trick is a barbed seed. 



XI. Hydrotropism may be shown by the following experiment. 

 Take a small box like a cigar box and remove the bottom and put on 

 instead some wire gauze and fill it with soil. If a seed is planted and 

 germinates, the roots will come through and project beyond the wire; 

 but if the ground is well saturated the roots will turn again and curve 



