144 THE NATURE STUDY COURSE. 



their transpiration. When plucked such plants wither slowly. 

 Technically they are called xerophytes. 



Plants that love damp soil and moist air and are hence 

 called mesophytes or hyyrophytes, usually have large or very 

 many thin leaves with numerous pores that transpire freely. 



Trees and other plants with deciduous leaves are called 

 tropophytes because they turn from a condition in summer 

 when they require and transpire much water to one in winter 

 when they use little. Plants that nourish on salty or alkaline 

 lands are called halophytes. They also have their peculiar 

 characteristics ; they strongly retain their hard-earned water 

 in ways similar to desert plants. 



Where the Roots Drink. — Plants with wide branches and 

 ample flat leaves shed the rain like an umbrella and carry it 

 away from the central axis. Some plants have semi-erect 

 leaves and channeled petioles and direct the rain towards the 

 stem. Infer the differences in the root-spread of these kinds 

 of plants. In this respect compare the beet and Indian corn 

 with the potato and sunflower. 



Relations to Light. — Observe the struggle of plants to 

 reach the light. The dandelion and plantain press their 

 leaves close to the ground to prevent other plants from 

 growing up around them and shutting off their view of the 

 sun. Contrast two trees of the same species — one growing in 

 the open field, with another in the thick forest. Note how 

 the leaves and flowers of some plants follow the sun from morn 

 till eve, also how leaves that are bunched or rosetted vary the 

 lengths of their petioles to bring every leaf -blade into the 

 light. A pumpkin vine partly in the open ground and partly 

 among long grass affords an instructive study. The leaves of 

 house plants not regularly turned become strongly " drawn " 

 to the light. 



