CHAPTER IV. — MOVEMENTS OF PLANTS. 247 



branch will have been very slowly thawed. Now compare its condition with 

 that of the other branch. One is comparatively uninjured and may even be 

 made to grow, while the other is completely wilted and cannot be revived. 



Try a similar experiment with two potato tubers. 



6. Obtain in autumn or late summer some seeds of the common Dodder, 

 a parasite. Plant them in a flower-pot and cause them to germinate, keeping 

 the temperature of the pot at about 85^ F. Examine the embryo of one of the 

 seeds after germination has begun. It looks like a simple coiled thread, no 

 cotyledons being developed, although it belongs to the great sub-class of Dico- 

 tyledons. In becoming a parasite it has apparently forfeited its seed leaves, 

 and it will be observed as the embryo develops, that it forms no true leaves. 

 It is in fact all stem, and even this seems modified into a tendril. Observe the 

 slender, thread-like stems push out of the soil and circumnutate in search of a 

 support. If no living stem or leaf be found to which they can cling, they soon 

 wither away, for no chlorophyll is developed in them, and they are therefore 

 incapable of assimilating mineral food ; but if some green plant be placed near, 

 they will soon twine about it, sending sucker like roots into its tissues, and 

 growing rapidly by deriving nourishment from it, perhaps even destroying the 

 life of their host. 



CHAPTER IV 



Movements of Plants. — Sensitiveness of Plants. 

 Reproduction. 



Movements of Plants. Although some plants, like the so- 

 called Rose of Jericho, wither during the dry season and are 

 blown by the wind, often to great distances over the sandy plains, 

 but resume their verdure and send forth blossoms when they 

 reach moist soil, or at the advent of the rainy season, strictly 

 spontaneous movements of transition or locomotion are confined, 

 as we have already stated, to the flowerless plants, and are most 

 conspicuous among the lowest forms. They are exhibited chiefly 

 by isolated cells, or by small colonies of cells. This is not 

 because the protoplasm of higher plants has really less activity, 

 but rather because it is mainly confined within rigid walls, so 

 that the young and growing parts, or those, at least, in which the 

 cell walls are thinnest, are the only ones free to move. 



Locomotion in plants exists under three modifications, the 

 a?nceboid, the ciliary, and a creeping motion of ill-defined char- 

 acter, such as that observed in many Diatoms, Desmids, etc. 

 Plants that exhibit amoeboid movements are unicellular and 



