330 THE CROSSING OF FLOWERS. 



ing stigma is, in the next instant, smothered in pollen over its proboscis, head, and 

 thorax. Cross-pollination must ensue if this bee shortly after visits the flowers of 

 another plant, and wherever Heaths which flower simultaneously grow together 

 there is no lack of hybridization. Whether the stigma of a flower is pollinated by 

 bees with pollen of another plant of the same or of another species or not at all, it 

 always begins to wither in two days' time and ceases to be receptive. The stamens 

 in the same flower now elongate and push their anthers out of the corolla mouth. 

 The restriction being removed the anthers separate, and pollen will fall out of 

 their compartments at the slightest movement (see fig. 295^). The merest swaying 

 of the flowering branch is suflficient to cause the pollen to fall. The still receptive 

 sticky stigmas of the younger flowers on the same branch, and indeed of flowers on 

 other branches of the same plant at some distance, are thus necessarily pollinated 

 with the dust-like pollen. 



In the inflorescence of the Toothwort (Lathrcea Squamaria) the crossing is 

 effected in exactly the same way. The flowers, like those of the Heath, are all 

 turned towards the side from which insects may be expected to arrive (see fig. 295 ^). 

 They are protogynous, and the ripe stigma projects beyond the margin of the corolla 

 before the latter has properly opened and when the anthers below are still closed 

 (see figs. 295 6,7,9), ^.^ this stage the stigma can only be pollinated with the pollen 

 of other plants whose development is further advanced. Corolla, style, and filaments 

 continue to elongate, the style, which has hitherto been bent like a hook, straightens, 

 the stigma, which was formerly in front of the narrow entrance to the flower, takes 

 a higher position, the anthers dehisce, and the flower now enters upon its second 

 stage (see figs. 295^ and 295^*^). Pollination is effected at this time by insects. 

 Humble-bees suck the honey secreted by a succulent cushion below the ovary, and 

 so transfer the pollen of the Toothwort from flower to flower. When they come to 

 a flower they brush against the projecting stigma and deposit pollen on it which 

 they have gathered elsewhere; they then push their probosces between the anthers, 

 which are held together by soft hairs. They are obliged to take this path, for 

 otherwise they would soon come to grief. The filaments below the anthers are 

 studded with little pointed thorns (see fig. 295^°), and the humble-bee carefully 

 avoids any contact with them. He therefore passes between the contiguous anthers 

 of the sprinkling stamens (cf. p. 271), separating them slightly, and thus causing a 

 fall of dusty pollen which covers his proboscis and head. And now comes the third 

 and last stage. The style and stigma wither and dry up, and the stamens elongate 

 and push their anthers beyond the margin of the corolla (see figs. 295 ^^ and 295 ^''). 

 The anthers no longer cohere. The pollen retained in their cavities is carried awa}' 

 by the wind, and will be deposited in part on the still receptive stigmas of neigh- 

 bouring, younger flowers. If a flower has already been visited by a humble-bee 

 very little pollen will remain in its anthers, but if there has been no insect-visit the 

 anthers are full of pollen when they are extended from the flower, and this is wafted 

 in small clouds to the stigmas of the younger flowers in the upper part of the spike. 

 Here again, as in so many instances, geitonogamy does not supervene till towards 



