PROTECTION OF POLLEN. 



125 



of moisture is increased the anthers will close, remain shut throughout the night, 

 and not begin to open again till after sunrise, when the degree of moisture is 

 diminishing. 



In cases where both the anthers and the petals of a flower open and close 

 periodically, the corresponding movements are for the most part accomplished 

 simultaneously; but if the cause of the movement is different for petals and 

 anthers it may happen that there is no such unison. For instance, after 

 prolonged rain, the petals of Bulbocodium may open under the influence of a 



Mi 



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« 









1 



^ 



Fig. 226.— Protection of Pollen. 



'Flower of the Bulbocodium with the perianth and the anthers open as they are when the sun is shining and tlie air dry. 

 2 An anther from the same. 3 Flower of Bulbocodium in moist air ; the perianth half open, the anthers closed. * An anther 

 from the same. 6 Flower of the Lady's Mantle (Alchemilla) with its anthers open in a dry atmosphere. 6, 7 Antliers from 

 the same, s Flower of the Lady s Mantle with its anthers closed in rainy weather. ^, i" Anthers from the same, n Flower 

 of the Bay Laurel (Laurus) with its anthers open in a dry atmosphere. 12 An anther from the same, is Flower of the 

 Bay Laurel with its anthers closed in wet weather. 1* An anther from the same. 15 Staminiferous flowers of Junipanis 

 Virginiana in a dry atmosphere. 1^ The same magnified, i? Staminiferous flowers of Juniperus Virginiana in wet 

 weather, is The same magnified. 1, 3, is, 17 natural size. The rest x 2 to 8 times. 



warm spell of sunshine, whilst the anthers still remain closed owing to the excessive 

 moisture of the atmosphere. 



Anthers close up much more quickly than petals on the approach of danger. 

 They usually take only a few minutes, and in many cases not more than half 

 a minute. The anthers of the Bastard Toad-flax {Thesiwm alpinum) shut up 

 within thirty seconds of their being moistened. In this plant the process of 

 closing is rendered additionally interesting by the fact that the moistening of 

 the anther-walls is effected by peculiar tufts of hairs projecting from the perianth. 

 The briefest possible description of this phenomenon will be given here. The open 

 flower of Thesium has the limb of its perianth turned to the sky. This position 

 is maintained unchanged day and night, and even the occurrence of bad weather 

 does not cause any alteration in the direction of the flower-stalks or the position 

 of the flowers. Hence rain-drops falling from above and the dew formed on 



