4 MOVEMENTS OF PLANTS. 



been accomplished in the study of the movements of plants, 

 and the whole subject of plant-motion is one of great in- 

 terest, and of great importance in its scientific bearings. 



The descent of the root into the earth, the ascent of the stem into 

 the air, and the turning of the branches and leaves towards the light, 

 observed in plants generally, are all regarded by botanists as spon- 

 taneous movements, although imperceptibly slow. 



Some kinds of plants, as the Sensitive Plant (Mimosa pudica), exhibit 

 a sort of sensitiveness or irritability when somewhat roughly touched, 

 and, at such times, they suddenly change the position of their leaves 

 or leaflets, quickly folding them more or less completely, as they do at 

 night. 



There is one kind of plant, Venus's Fly-trap (Dioncea musdpula), of 

 North Carolina, which has such a degree of sensitiveness and power . 

 of rapid movement, that the moment a fly or other insect alights upon 

 the curious appendage which each leaf bears at its summit, the "trap" 

 closes, often capturing the insect, pressing it harder and harder the 

 more it struggles, and thus, in many cases, depriving it of life. 



As examples of rapid movements of plants which are apparently, if 

 not really, independent of any external force or excitation, it may be 

 mentioned that the spores of many kinds of algae move spontaneously 

 in the water when they are first discharged from the parent cells in 

 which they originate, and hence they appear very much like minute 

 infusorial animalcules. The movements are made by means of exceed- 

 ingly minute hair-like appendages or cilia, having the closest resem- 

 blance to the vibratile cilia of infusoria. Again, many kinds of micro- 

 scopic algae, well known under the name of Desmids and Diatoms (Fig. 

 2 5 ), move freely about in the water, even in their adult state. And, as 

 an example of flowering plants which apparently exhibit spontaneous 

 movements, we may mention the Desmodium gyrans of the East 

 Indies, a leguminous plant, with trifoliate leaves, which has the two 

 lateral leaflets continually rising and falling, by a succession of jerks; 

 and one leaf rises ichile tlie other falls ! 



In view of the facts now stated as modifying the defi- 

 nitions of animals and plants, as given above, it appears 

 that if we would give definitions to which there are no 

 exceptions, we can hardly say more than that Animals are 

 living beings which are nourished and built up wholly by 



