9 



ASSOCIATION OF ORGANISMS THE WEB OF LIFE 



kinds of arrangement we may take the common wild Monkey- 

 Musk (Mimulus luteus, fig. 1081) as an interesting example. An 

 insect visiting this flower first touches the bilobed stigma, which 

 receives any pollen that the visitor may bring. But the stigma is 

 very sensitive to contact, and immediately closes, almost like a 

 book, remaining in this state for some time. Hence it does not 

 receive from its own flower any of the pollen with which the 

 departing guest has been loaded. 



It ought, however, to be stated that some flowers are regularly 

 self-pollinated, while others exemplify a number of most ingenious 

 devices for effecting this as a last resort. The whole structure of 



Fig. 1081. Pollination of Monkey Musk (Mimulus lutens). i, External view of flower; 2, same in longitudinar 

 section, with open stigma; 3, ditto with closed stigma. 4, Pollen is deposited on the lower lip of the stigma by a 

 proboscis passing in the direction of the arrow; 5, the stigma has closed, and the proboscis passing on opens the 

 closed anthers and becomes covered with pollen ; 6, proboscis being withdrawn in direction of arrow, but does 

 not deposit pollen on the stigma as this is closed, i, 2, and 3, natural size; 4, 5, and 6, somewhat enlarged. 



a Foxglove flower, for example, is wonderfully adapted to cross- 

 pollination by humble-bees, but after a time the purple corolla falls 

 off, and in so doing drags the stamens attached to it over the 

 stigma, so that this is self-pollinated, and if it has not already 

 received foreign pollen, the egg-cells will be self-fertilized. Full 

 details of this sort of arrangement will be found in Kerner and 

 other botanical works, but would be out of place here. It is 

 perhaps desirable to add that some authorities believe the im- 

 portance of cross-pollination to have been somewhat exaggerated. 

 DEFENCES OF FLOWERS AGAINST UNBIDDEN GUESTS. The 

 animals which are most serviceable as agents of cross-pollination 

 are those capable of carrying pollen from one plant to another, 

 though interchange between flowers on the same plant is beneficial 

 to a lesser degree, and is often the chief kind of crossing which 

 takes place in cases where a considerable number of small flowers 



