84 Flowers and their Unbidden Guests. 



■whole flower; fig. 102, longitudinal section of lower 

 part of tube). In Veronica officinalis tlie " weel " is 

 placed at the mouth of the tube, but, as the tube is 

 very short, is stOl only just above the nectar which it 

 protects (Plate III. fig. 94, longitudinal section; fig. 

 93, front view of the flower). The trichomes which 

 constitute the weel do not always form a complete 

 circle round the corolla, but are frequently given 

 off only from one side ; in which case however they 

 are so long as to extend over the whole central space 

 of the tube. This, for instance, is the case in Veronica 

 Chamcedrys (Plate III. fig. 91, lateral view of corolla; 

 fig. 92, longitudinal section of same). 



In Passion-flowers the whole corona constitutes a 

 single, double, or treble "weel," as may be seen very 

 beautifully in the section of the flower of Passiflora 

 vespertilio (Plate III. fig. 81). Lastly, a very remark- 

 able weel-formation is to be found in many lilies (e.g. 

 Lilium chalcedonicum), and in several gentians, especi- 

 ally of the genera Ophelia and Swertia. The nectar is 

 here secreted in certain pit-like depressions on special 

 epiblastemes of the corolla ; and the annular margin of 

 each depression is broken up into a fringe of hair-like 

 processes, whose points converge, and which twist and 

 interlace so as to form a kind of cage over the necta- 

 riferous pits (Plate II. Swertia per ennis, fig. 67, longi- 

 tudinal section of flower ; fig. 68, lower part of the petal, 

 with its pair of nectariferous epiblastemes ; fig. 69, longi- 



