656 PHYSIOLOGY. 



pollen-mass to the needle &c. Then occurs, first a divergence of the two 

 pollen-masses one from the other, and subsequently a depression, so that 

 they assume a nearly horizontal direction (fig. 018, b). In this position they 



Fig. 618. 



Orchis pyramidalis : a, pollen-mass just removed from the anther, vertical ; 

 b, pollen-maases divergent and horizontal. 



are so placed as to come into contact with the V-h'ke stigmata of another 

 flower, and thus effect cross-fertilization. 



Style : Goldfussia anisophylla, Martynia, Mimulus, &c. 



Movements of Stems. Some plants manifest a series of spon- 

 taneous movements, as Ceratophyllum, where the stem exhibits 

 regularly movements of bending and straightening. The young 

 growing shoot of Abies Nordmanniana has been observed to revolve 

 irrespectively of the sun's movements, and the terminal shoots of 

 the Deodar have similar movements. 



Climbing Plants. The phenomena of the movements of climb- 

 ing plants, including the spontaneous revolving movement of ten- 

 drils &c., and those dependent on contact, have been studied in 

 detail by Mr. Darwin, who has shown that organs of the most 

 diverse morphological character may nevertheless exhibit the same 

 phenomena. The object is to enable the plant to expose its leaves 

 to the light and air with little expenditure of material. In this 

 way a weakly growing plant can maintain itself in the struggle 

 with trees and vigorous growing plants. Darwin divides climbing 

 plants into four classes : 1, those that twine spirally in a dex- 

 trorse or sinistrorse manner round a support ; 2, those endowed 

 with irritable organs which when they touch any object clasp it ; 



3, plants climbing by means of hooks, as some Palms, Brambles, &c. ; 



4, plants climbing by means of rootlets, as the Ivy. 



The two first Classes exhibit special movements. The young growing 

 shoots of climbing plants, and, as we have seen, of Conifers and probably 

 most other plants, if watched for a continuous period, or observed at in- 

 tervals, may be observed to bend to one side, and to travel slowly round to 

 allpoints of the compass in succession, the revolving movement, which goes 

 on by night as well as by day, varying in rapidity according to circum- 

 stances and ultimately ceasing. The revolution is effected by a bending 

 over of the stem first in one direction, then in another, so that the re- 

 volving stem sweeps round; but does not become twisted so long as it is 



