122 PROTECTION OF POLLEN. 



when there is no longer any pollen to protect from rain and dew, they remain 

 erect. 



All these phenomena of inflection and straightening on the part of flowering 

 axes and inferior ovaries are brought about in the same way as the periodic 

 movements of petals and bracts by alterations in the tension of the tissues. 

 These variations of tension are again due partly to vicissitudes in respect of 

 heat and light, and of the degree of moisture of the air. But mechanical 

 stimuli also play an important part, especially such shocks to the flower-bearing 

 axis as ai-e occasioned by the incidence of drops of rain and by gusts of wind. 

 The fact that drops of water are found resting on the nodding or drooping 

 flowers, if the latter are examined before sunrise when there is a heavy dew, or 

 after a shower, tempts one to look upon the inflection merely as a consequence 

 of the strain imposed upon the stalks by the increased weight of the water- 

 laden flowers. No doubt this sti-ain has something to do with the inflection, 

 but it is equally certain that the drooping state does not disappear at once 

 when the water has evaporated and the strain due to its weight has terminated. 

 This persistence of the inflection at all events must be attributed to an alteration 

 in the tension of the tissues of the stem, and no more than the first impulse 

 can be derived from the weight of dew or the impact of drops of rain. 

 Additional evidence of this is afforded by the facts that the process of bending 

 is set up by rain falling on flowers and stem, even when it rolls off" immediately, 

 and that pedicels and peduncles also bend over whenever the entire plant is 

 caused to sway about by the wind which precedes a downpour, the stems on 

 these occasions always curving away from the direction of the wind, or, to use 

 a nautical expression, to the lee side. 



This phenomenon of the bending of stalks and drooping of flowers before 

 the rain has actually begun looks almost as if the plant had the power of 

 foreboding the approach of bad weather and of adapting itself beforehand in such 

 a manner as to prevent any injury being subsequently inflicted ujDon it by 

 that destructive agency. Such is the opinion of the peasantry in parts of 

 Europe, and they look upon the inflections above described, as well as the 

 closing of the heads of the Carline Thistle, which was mentioned further back, 

 as a sign of imminent rain. There is, however, as already said, a mechanical 

 explanation of the phenomenon dependent on a change in the tension of the 

 tissues of the stem induced by the oscillations of the plant when subjected to 

 the gusts of wind which usually precede rain, the change of tension being 

 manifested externally by the persistence of the stem's inflection. Moreover, this 

 lasting curvature of the stem may also be produced artificially by inducing 

 the same kind of strain as is caused by the weight of the rain-drops or the 

 vibration caused by rain and wind. If, for instance, you bend the pedicels of 

 various species of Oxalis from the erect position they occupy in the middle of 

 tlie day and hold them down for a time, or if you shake or knock them, the 

 tissues forthwith undergo a change of tension which results in those stalks 



