CHAPTER V 



have a bloom on their under side, which sheds the dew at the slightest 

 disturbance. Do not fail to have children notice that dew collects on 

 the lower, as well as on the upper side of leaves. The fact that dew 

 remaining a long time on plants, hinders transpiration, will be brought 

 out in the next chapter. Pentstemon cordifoliu-s, a plant sometimes 

 called wild honeysuckle, pictured in Fig. 71, puts out leaves in early 

 winter. This is a climbing, or perhaps more properly, a weaving 

 plant, and it is easier to see its method of getting up in the world now, 

 than when it is in full foliage. It sends out some new shoots that 

 seem to be pushing upward for support, but shoots from branches that 

 have already looped themselves over a supporting twig of some other 

 shrub, often continue on in a horizontal position, and the different 

 disposal of leaves on these two sorts of shoots, is very marked indeed. 

 The leaves are opposite, and on the vertical stems they stand at right 

 angles with the stem, in four orderly lines, an arrangement advan- 

 tageous for short petioled, broad-based leaves, so long as stems are 

 vertical. But when the shoots are horizontal all of the leaves twist 

 on their petioles sufficiently to face upward, and the leaves of the 

 alternate pairs bring themselves into the same plane as the other 

 pairs, neatly filling in the interspaces. This is a common habit of 

 plants with opposite leaves, and it will not be difficult to find other 

 illustrations. The fact that the poison oak sometimes climbs like the 

 English ivy, by aerial rootlets, should be noted. The new leaves and 

 shoots of the poison oak, Pentstemon, and many other plants, have a 

 very noticeable amount of red coloring matter, or anthocyanin. As 

 stated before, this color in stems and veins is supposed by some botanists 

 to act as a screen, protecting the various products that pass along these 

 routes; and it seems to be fully proved that, by changing light to heat, 

 anthocyanin is of special service to young leaves. 



By this time the buds on many of the trees may be somewhat 

 swollen, particularly on the willow, sycamore and alder, and the 

 alder is probably in flower. It is easy to see why it is an advantage 

 for the flowers of wind pollinated trees to develop before the leaves. 

 The willows are pollinated by bees as will be shown later. It is very 

 desirable indeed for children to take a first lesson in pollination from 

 the willows. Much of the observation called for in the chapter on 

 the " Awakening of Trees," must be carried on beforehand. The 

 teacher should, if possible, select trees that can be watched without 

 special excursions ; the next best plan is to have twigs that show 

 signs of activity brought to the schoolroom and kept in water. 



