ASSOCIATION OF ORGANISMS THE WEB OF LIFE 



so situated that insects creeping up the stem are sure to find it. 

 As soon as the Balsam begins to open its flowers nectar is abun- 

 dantly secreted by these nectaries, and being both abundant and 

 more accessible than that in the flowers, unwelcome guests are 

 diverted from these. Regarding this sweet fluid and its use Kerner 

 makes the following remarks: " The honey-loving ants lick it up 



eagerly, and are content not to 

 stray farther upwards. Actual 

 observation shows that the 

 flowers of Impatiens tricornis 

 are free from ants, whilst these 

 stipular nectaries are much fre- 

 quented by them. Their pres- 

 ence in the flowers is very un- 

 desirable, since they could readily 

 get at the honey there without 

 touching the pollen or stigma. 

 And more than this, they would 

 not only pilfer the honey, but 

 they would also drive away those 

 winged insects for which the 

 honey is prepared the welcome 

 guests that pollinate the flowers. 

 We are justified on the facts in 

 regarding this diversion of the 

 unbidden guests as an indirect 

 protection of the floral honey." 



Insects are not infrequently 

 prevented from reaching the 

 flowers by means of a watery 

 barrier. This is obviously so in 



the case of water-lilies and other aquatic plants, and may also be 

 observed in some land forms. In Teasels, for example, the leaves 

 are arranged in pairs, the bases of each pair being united together 

 to form a sort of cup, in which water collects, so as completely to 

 surround the stem (fig. 1082). 



Slippery surfaces are often present, on which creeping insects 

 can find no foothold. There is sometimes a smooth coating of 

 wax, as in certain Willows, where the catkin-bearing twigs are 

 thus protected. Another interesting case is that of the Snowdrop 



Fig. 1082. A Teasel {Dipsacus laciniatus], showing 

 water-cups formed by fusion of bases of leaves 



