RESULTS OF POLLINATION. 



285 



branches in Compositse, and whicli at first sight might be mistaken for stigmatic 

 papillae, do not deserve this appellation. Their function is only to sweep the pollen 

 out of the anther-tube, and their significance will be repeatedly spoken of later in 

 the chapter devoted to autogamy. 



The deposition of pollen on the stigma is followed not only by alterations in the 

 pollen-cells and in the stigmatic tissue, but also in other parts of the flower, espe- 

 cially the corolla. The visible changes in the stigma are the withering, shrivelling, 

 and turning brown of its superficial cells. In those plants described above, on 



Fig. 282.— 1 Fhysostigma vcnenosum. = Pistil of this plant, removed from the flower ; magnifled. a Flower of Swietenia 



Mahagoni. (After Baillon.) 



whose sticky stigmas the pollen is not immediately stimulated to send out pollen- 

 tubes, weeks sometimes elapse before these alterations occur; in others, however, 

 they are to be observed in a few hours. Solanaceous plants are very noticeable in 

 this respect, especially Nicandra physaloides, and the Deadly Nightshade {Atrojya 

 Belladonna). An hour after pollen is deposited on the sticky stigma, it begins to 

 wither and turn brown, and the whole style alters and drops oif the ovarj''. Here, 

 then, the pollen-tubes must have been emitted as soon as the pollen-cells came in 

 contact with the stigmatic tissue, and they reach the ovules in the interior of the 

 ovary within a few hours. 



The changes which occur in the petals are even more noticeable. As soon 



