BOTANICAL SUBJECTS. 817 



XVI— SPUES. 



Are the spurs or hollow cones we find on the petals of certain 



plants brought about by the agency of insects, or by natura 

 selection ? 



There is reason to suppose that both insects and natural 



selection may influence the increase of a spur, but that it can be 

 formed all of a sudden, independently of those agencies, does not, 

 I think, admit of a doubt. 



Fig, 135. Saccate petals of Blumenbachia coronata. 



Blumenhachia coronata, Fig. 135, has saccate petals. One 

 can easily conceive that these sacs once formed, especially if their 

 interior secretes some liquid, might readily be increased by the 

 probings of insects, and therefore also through natural 

 selection. 



The saccate petal of Calochortus pulchellus, once formed 

 might also, by the same agency, be easily lengthened into a long 

 spur, like those of Aquilegia. What is difficult to account for 

 supposing that spurs do so commence, is a whole whorl becomino- 

 saccate or spurred at the same time. 



Fig. 136 shows the saccate glume of Briza minor, which also 

 might easily be conceived as forming the beginning of a 

 spur. 



