114 Flowers and their Unbidden Guests. 



i 

 labellum. The entrance to this, in itself far from wide, 



is still further narrowed, and this considerably, by a 

 swelling at the mouth of the pouch. This swelling or 

 fold forms an oblique bar at the back part of the 

 labellum, itself narrowed into a funnel, and reduces the 

 diameter of the entrance to half a millimetre. This 

 effectually prevents most wingless insects from creeping 

 in and getting at the nectar ; and even amongst flying 

 insects only such are apparently adapted to the flower as 

 have a thin suctorial trunk, in using which they would 

 unavoidably carry off the adhesive pollinia, and forthwith 

 transport them in their roving flight to other flowers. 



In the various species of Galeopsis the corolla pre- 

 sents two projections at its mouth. I have tried to 

 give a representation of these in Plate II., fig. 56 

 (Galeopsis graindiflm-a). The corolla-tube is 23 mm. 

 in length, and in its lower half is not more than 

 2-3 mm. in width; but the upper half widens 

 out and forms a funnel, which is pretty nearly 4 mm. 

 in diameter at its anterior opening, that is at the 

 throat of the corolla. The width of the mouth of 

 the corolla on the other hand, that is the distance 

 which separates the margin of the upper lip, and there- 

 fore the anthers and stigma which it conceals, from 

 the flat median portion of the lower lip, is no more 

 than 2 '5 mm. If then the corolla were made of very 

 firm tissue it would be impossible for a humble-bee, 

 on visiting the flower, to thrust its head and thorax, 



