ROBERTSON FLOWERS & INSECTS, ASCL. TO SCROPH. 583 



SOKOPHULARIACE^:. 



Verdascum Thapsus L.- ("Nat, from Eur.") — In a paper on 

 "Zygomorphy and its Causes."* I have assumed that when the 

 perianth of lateral flowers failed to protect the stamens, either 

 on account of its shortness or its wide expansion, insects would 

 alight upon the stamens in preference to other parts of the flower, 

 and in this way I endeavored to explain the origin of flowers 

 which dust the visitor upon the ventral surface. It was my de- 

 sire to discuss the irregularity of Verbascum in connection with 

 that of ScropJuilaria^ but I could not venture to do so because I 

 had made no direct observations upon it, and because the obser- 

 vations which had been made by Miiller did not clearly conform 

 with my views. I have also criticised Prof. Henslowj for claim- 

 ing that Verbascum is in the first stage of irregularity, but I was 

 not then prepared to assert that the quotation which he made 

 from Miiller did not describe the true relations which visiting in- 

 sects hold to ditferent parts of the flower, indeed, my statements 

 rest upon the observation of V. Thapsus and Blattaria alone, 

 and upon inferences drawn from Miiller's lists. 



I suppose the prototype of Verbascum to have been a bilabiate 

 flower with didynamous stamens, because the type of the order 

 is didynamous and because the two genera which with Verbas- 

 cum form the tribe Verbascece have only four stamens. The 

 flower was originally adapted to long-tongued bees which visited 

 it for nectar, alighting upon the lower lip and striking their 

 backs against the anthers. The stamens were included, holding 

 their anthers against the upper wall of the corolla in such a posi- 

 tion that flies and small bees would hardly be able to get at the 

 pollen. Then the flower became more widely expanded, expos- 

 ing the stamens so that the insects could easily alight upon them 

 and eat or collect the pollen. The fifth stamen, being no longer 

 ci-owded in the upper part of a narrow tube, regained its anther- 

 iferous function and joined the other four in their new position on 

 the lower side. Then the flower, being fertilized mainly by in- 

 sects coming for pollen, began to reduce its nectar supply. 



* Bot. Gazette xiii. 146, 203, 224. 



t Bot. Gazette xiii. j2).; xiv. 134-36. And Henslow: Origin of Floral Strnctures, iiS. 



