34 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



THE MOVEMENTS OF PLANTS. 

 By Eev. George Henslow, M.A., F.L.S., &c. 

 [Delivered June 9, 1896.] 



Introduction. — The old distinction between animals and 

 plants, that the former could move and the latter could not, was 

 based on very limited observations. For, not only have very 

 many of the lower forms of vegetable life motile reproductive 

 bodies, as the zoospores of the Potato fungus and Alga?, but even 

 all the higher plants can move their various organs, though they 

 be rooted in the ground. The object of the lecture was to 

 illustrate this fact by a small selection of characteristic examples. 



Motions of plant-organs can be either the result of and during 

 growth, as in the development of leaves during the expansion of 

 leaf -buds ; or the result of certain irritations taking place 

 periodically or otherwise, after the organ is completely formed, 

 as in the foliar sleep of plants, in flower-stalks, &c. Excepting 

 the bursting of capsules and other cases, where usually life is 

 extinct, the motions are due to the inherent properties of living 

 protoplasm. 



Geotropism and Circumnutation. — The first evidence of 

 germination in seeds is seen in the protrusion of the radicles, and 

 in all ordinary dicotyledons growing in the soil the apex elongates 

 and forms the tap-root which grows downwards, i.e. in the 

 direction of the action of gravity, this being the exterior exciting 

 force. Darwin found that the tip of the radicle of a cabbage 

 seed was only acted upon by gravity upon its " growing point," 

 i.e. for a' length of from "02 to '03 inch ; but the influence can 

 be conducted to some higher point where the bending may take 

 place. The property of an organ growing or bending under 

 the influence of gravity is called " Geotropism," or "turning 

 earthwards." When the cotyledons appear above the soil by the 

 growth and elongation of the radicle (the plumule being for a 

 time arrested), the radicle now takes the name of 41 hypocotyl," 

 being " below the cotyledons." If the radicle be arrested while 

 the plumule begins at once to grow, as in the bean, the plumule 

 is now called the " epicotyl," as it is " above the cotyledons." 



