ADJUSTMENT TO TEMPERATURE 



119 



it is possible that the period or time of flowering, the structure or 

 position of the flower, may result in a certain degree of protection. 

 The stigma, while in a receptive condition, must be guarded against 

 excessive dryness, and also perhaps against rain. This is usually 

 brought about by the same devices that insure the protection 

 of the pollen. Finally, the pollen must be guarded against those 

 insects which w^ould devour it without effecting its transfer. This 

 result is usually obtained as a secondary consequence of modifica- 

 tions for insuring pollination. 



142. Structural protection. The devices which serve to protect 

 pollen are of three sorts: (1) morphological, (2) mechanical, (3) 





Fig. 29. Structural protection of \mA\v\\ in the hi'iirhcrry, A rrtostaphylus 

 uva-ursi, by means of the inverted fiask-.shapecl corolla. 



seasonal. The first and third, as a rule, accomplish protection 

 incidentally. Structures of the second class prol)al)ly owe their 

 very existence to the necessity for protection of the pollen. Mor- 

 phological contrivances are purely structural or positional. To 

 the first class belong all flowers in which protection results from 

 the structure or shape of the flower, of the flower parts, or of the 

 flower cluster. Protection of this sort may arise from l he st ructure 



