PAMMEI, — POLLINATION OF PIILO.MIS TUBEROSA. 261 



is well shown by the list of flowers which Bomhus masfrncatus 

 visits. 



Flowers grown in large masses are conspicuous, and therefore 

 attract many insects; and, as the perforated tlowers usually con- 

 tain considerable nectar, the number of insects visiting the flowers 

 at any one time is very large, and, as Darwin has shown, (25c and 

 28) some of the nectaries are sucked dry ; now, in order to save 

 time, for the flowers would have to be probed for their nectar, the 

 insect makes perforations. To this rule there are exceptions, as 

 has been shown in some of the cases cited, where an insect, 

 unable to get the nectar in a normal way, takes to perforating 

 flowers. Midler, Loew, and others, have shown that there is a 

 certain correlation between the length of the tongues of Hymen- 

 optera and the flowers they perforate, as can be seen bv consult- 

 ing their tables on flowers and their visitors. 



I have enumerated enough cases to show why flowers, and esjDC- 

 cially those with deep-seated nectar, are perforated, and shall 

 now consider briefly the protection against such unwelcomed vis- 

 itors possessed by some such flowers. 



Delpino recognizes three principal modes of protection : 



1. The coriaceous thick hard tubular calyx sometimes found surrounding 



the region of the nectar receptacle. 



2. Inflated organs, like the calvx o'l Rki7ianthus and the involucre of Con- 



volvulus septum. 



3. A hooded or spurred calyx enclosing as a second envelope the nec- 



tariferous spurs, as in Delphinium^ and still mo' e etYectively in 

 Acoiiitum. 



It will be well to consider these structures somewhat in detail. 



In Rhinanthus alectorolophus there is at least a partial protection, 

 as the calyx is inflated and the arch of the corolla is firm and 

 smooth. Midler (90 e) observed a female of Bombus mastrucatus 

 making unsuccessful attempts to bite holes in the tubes of the 

 corolla of this plant. Ptdicularis vertirillata is also somewhat 

 protected, as the calyx is globular, smooth, and compressed later- 

 ally, while the corolla has an abrupt rectangular bend within the 

 calyx, and the upper lip is very firm. Bombus mastrucatus and 

 B. terrestris (gob) both made several unsuccessful attempts on 

 this species. 



