PROCEEDINGS 



OF THE 



HERTFORDSHIRE NATURAL HISTORY 



SOCIETY. 



Okdinaet Meeting, 25th October, 1881, at Watford. 



George Eooper, Esq., F.Z.S., President, in the Chair. 



Mr. George Brightwen, The Grove, Stanmore ; Mrs. James 

 Currie, Hill Side, Watford; Mr. Marlborough R. Pryor, M.A., 

 F Z.S., Weston Manor, Stevenage ; and Miss Hooper, Nascott 

 House, Watford, were proposed as Members of the Society. 



The following lecture was delivered : — 



" The Movements of Plants." By the Rev. George Hcnslow, 

 M.A., F.L.S., r.G.S. 



The Lecturer commenced by remarking that the old distinction between 

 Animals and Plants, that the former could move, but not the latter, was no lonsjer 

 tenable ; for many animals such as sponges and oysters were fixed, but innumerable 

 minute alg* could move freely in water ; and that all plants, though fixed in the 

 soil, were constantly in motion as far as their aerial parts were concerned. 



Commencing with germinating plants, he described how the radicle first pro- 

 trudes, and then immediately "circumnutates," circumnutation being the word 

 which has been adopted to express a variety of movements of different kinds as 

 specially modified for different organs. It was a kind of "bowing around." 

 Simultaneously with this, geotropism or a tendency to turn in the direction of the 

 earth comes into play ; so that the radicle invariably turns towards the soil. 

 This downward force only acts upon the extreme tip of the radicle, which is 

 sensitive; an influence, however, is communicated to a point higher up, where 

 the radicle bends. The means by which the radicle penetrates the soil is neither 

 of these forces, but as soon as its root-hairs are formed, they become fixed to the 

 particles of earth, and so furnish a. purchase to the radicle, which now penetrates 

 by force of growth alone. 



The tip of radicles is also sensitive to moisture, so that it grows in the direction of 

 it, and this explains the so-called habit of roots to "seek" for water. Its most 

 remarkable property, however, is its sensitiveness to contact, so that if it meet 

 an obstacle a radicle deviates from it. This being the only known instance of 

 any plant-organ turning away from an irritant. As soon as the radicle gets past 

 the obstruction — say a stone — geotropism then causes it to go downwards once 

 more. Geotropism only acts with full influence on the central axial root. 

 Secondary roots are inclined at an angle to the first. If, however, this latter be 

 cut away, then the secondary ones turn downwards ; tlie tertiary rootlets are 

 uninfluenced by it, the result being that the entire mass of roots is spread out 

 in the best way for searching the ground for nourishment and water. 



VOL. II. — PART V. B 



