80G REVIEWS. 



cotyledons (with the elongation and protrusion of which the 

 germination of dicotyledonous seeds usually begins) circum- 

 nutates as soon as it conies out into the open air, and even 

 earlier: this is the earliest manifestation of an automatic 

 movement which is shared by all the succeeding portions of 

 stem developed from it, in the early life of most plants, 

 whether climbers or not. In the latter, and especially in 

 twining plants, we see this general faculty at its maximum 

 and in beneficial exercise. More remarkable and novel it is 

 to learn that the initial root, growing from the lower end of 

 the caulicle (not inaptly called by Darwin the hypocotyl'), also 

 shares in this faculty of circumnutation. As it penetrates 

 the soil in its downward course, it cannot largely manifest 

 this faculty, and indeed its power of circumnutation is always 

 small ; " but the circumnutating movement will facilitate 

 the tip entering any lateral or oblique fissure in the earth or 

 a burrow made by an earth-worm or larva ; and it is certain 

 that roots often run down the old burrows of worms. The 

 tip, however, in endeavoi-ing to circumnutate will (succes- 

 sively) press against the earth on all sides, and this can hardly 

 fail to be of the highest importance to the plant " (being sup- 

 plemented by another faculty, that of sensitiveness at the tip 

 presently to be mentioned) ; for " when the tip encounters a 

 stone or other obstacle in the ground, or even earth on one 

 side more compact than on the other, the root will bend away 

 as much as it can from the obstacle or the more resisting 

 earth, and will thus follow with unerring skill the line of least 

 resistance." Then, beside the almost universal heliotropic 

 movement, by which each leaf or leaflet presents its superior 

 surface to the direction of the greater light, Mr. Darwin 

 shows that these organs also circumnutate, beginning even 

 with the cotyledons or seed-leaves ; although their sweeps gen- 

 erally form so narrow an ellipse that they move up and down 

 in nearly the same vertical plane, a movement describing a 

 circle being converted into one up and down. 



These circu'mnutatory movements are of the most funda- 

 mental and therefore mysterious character. Although most 

 commonly connected with growth, they are at bottom inde- 



