244 TRANS. ST. LOUIS ACAD. SCIENCE. 



short-tongued insects visit only the small-flowered forms, which of 

 course cannot lead to cross-pollination. The genus Calamintha is 

 interesting in this respect. C. Clinopodium (82 d) is variable as 

 regards its gyno-dioecious character, and therefore presents all 

 stages. The American Calamintha Nepeta (no) is proteran- 

 drous. Mentha arvensis (82 e.), Thymus serpyUuin (82/., 26), and 

 other species belonging to these genera, are typically gyro-dice- 

 cious: so that, in this regard, Labiates are variable. 



The flowers of Phlomis tuberosa are adapted to pollination 

 by humble-bees, as has been shown, by the elastically hinged 

 arrangement in the upper lip and the length of the tube of the 

 corolla. Several of our species of Bombus must be able to do 

 efficient work in their cross-pollination, as the measurements 

 of their tongues indicate. Mr. Robertson, who has kindly identified 

 the insects I sent him, gives me the following measurements : 

 The tongue of a female of Bombus separatus measured 11 mm.; 

 while that of B. Pennsylv aniens was 16 mm. long. I frequently 

 saw a large species of Bombus, probably B. Pennsylv aniens, 

 which entered the flowers in a normal way, and most of the flowers 

 were pollinated by this insect. Besides this there was one other 

 humble-bee, a worker of B. vagans{ ?), which visited the flow- 

 ers, but mostly those which had previously been used by B. Penn- 

 sylvanicus. The tongue of this insect measured 6.5 mm., so 

 that it was hardly long enough to reach the nectar, and I doubt 

 whether the insect is strong enough to push the upper lip back 

 as it regularly visited the older flowers, no doubt it may be of 

 service to the plant. Anthophora and Melissodes, which have 

 longer tongues than those of Bombus Pennsylv aniens, are frequent 

 visitors to flowers with deep seated nectar, but they were not no- 

 ticed on Phlomis; on the other hand, Xyloeopa Virginica made 

 perforations and used them exclusively. I shall, however, call 

 attention to this in another part of the paper. 



The two species of Phlomis are much alike in the awn-pointed 

 lobes of the calyx, the hinged arrangement in the upper lip, and 

 the compactness of the flower-cluster. The flowers of Ph. Rns- 

 seliana are somewhat larger, and are therefore adapted only to 

 long-tongued insects, since the tube of the corolla is 20-22 mm. 

 long. But the tube of Ph. tuberosa is only 10 mm. long, so that 

 it is adapted to a much larger range of insects. Accordingly 



