go Flowers and their Unbidden Guests. 



smaller insects (Thrips alone excepted) to creep in and 

 reach the nectar. 



That the purpose of all these structures is the pro- 

 tection of the nectar from such insects as are too 

 small to conduce by their visits to cross-fertilisation, 

 is shown quite clearly by those Labiatae in which the 

 filaments and style are so elongated as to bring anthers 

 and stigma to a point considerably in advance of the 

 upper lip (Origanum, Thymus, Mentha, Lycopus). Here 

 no other insects than such as approach the flower on 

 the wing and from the side can possibly come into due 

 contact with the far-projecting stigma and anthers; 

 while such as come creeping up from below, and have 

 a body not more than 1'5 mm. in thickness, were no 

 barrier pub in their way, might steal in over the under- 

 lip, between and beneath the filaments and style, and 

 rifle the nectar without so much as touching stigma 

 or anthers, which would be in advance of them during 

 their whole visit. In such case the nectar would be 

 elxpended to no purpose. But it will be found that in 

 all such Labiatse, in all, that is to say, which are charac- 

 terised by far-projecting anthers and stigma, the corolla 

 is invested with a thick fleecy covering of trichomes, 

 by which small and creeping insects are effectually 

 excluded. 



The "weels" and tangles of trichomes which we 

 have as yet been considering effect the complete exclu- 

 sion of unbidden guests from the recesses of the flower, 



