124 Flowers and their Unbidden Guests. 



the bundle, form a fold. This fold encircles a narrow 

 passage, having an external orifice no more than 

 0'8-l"0 mm. in diameter, and communicating inter- 

 nally with a cavity, 7 mm. in length by 6 mm. in 

 width, placed behind the outgrowth. This cavity 

 contains abundant nectar, secreted by a disk that 

 surrounds the base of the style ; and into it large 

 flying insects can readily introduce their proboscis 

 through the above-mentioned narrow passage, whUe 

 no access is possible to small, and therefore unprofit- 

 able, visitors. A very minute insect, less even than 

 0'8 mm. in diameter, might, it is true, creep in through 

 the passage ; but were it to do so, it would be drowned 

 in the copious nectar, which completely fills the rela- 

 tively large cavity. 



In many cases it is not the androecium nor the 

 corolla, but the calyx, the epicalyx, and the bracts, 

 that by their contorted growth, by their dilatation, or 

 by their being crowded together, protect the nectar 

 from being unprofitably expended. In many Silenese, 

 for instance, the calyx is inflated to such an extent that 

 the nectary comes to be farther off from the calyx than 

 from the mouth of the corolla. It is thus rendered 

 impossible for certain insects to get at the nectar by 

 biting laterally through the perianth. It has long been 

 known, and the fact is common enough in the flora of 

 our country, that many Hymenoptera, and especially 

 humble-bees, instead of making their entrance by the 



