Guests, Welcome and Unwelcome 207 



have been a well-understood signal in its own country, 

 telling the small marsh-snails that their night quarters were 

 ready. These would dimb the stalk and find entrance by 

 a narrow opening at the base of the sheath, which would 

 soon after close upon them. Twenty-four hours later the 

 scent and warmth have much diminished, but then the 

 anthers open and drop down their pollen, not in separate 

 grains, but in chains or tassels of grains adhering together, 

 as much as an inch long, and far too bulky therefore to be 

 carried away by insects. On coming in contact with the 

 moist bodies of the snails, however, the chains separate 

 into grains, which adhere and are borne away when the 

 guests move on. 



And they are obliged to move on soon after the pollen 

 has fallen or else they would be suffocated; for the blos- 

 soms have been breathing vigorously in a confined space, 

 and so much carbon has been burned, and so much carbon 

 dioxide produced, that the bulb of the sheath is completely 

 filled with it, and a glowing match held within is extin- 

 guished. Such visitors as stay too long are therefore 

 safely suffocated, and thus prevented from eating the 

 young fruit, which they would otherwise do without fail. 



The prudent snails, however, having enjoyed their 

 warm bed and nectar, do not outstay their welcome; but 

 when these passing pleasures have come to an end, they 

 linger no longer, make the best of their way up the sheath 

 and down the long stem, and then proceed without delay 

 to climb some other plant whose blossoms are beginning 

 to give fragrant notice that another pleasant guest-chamber 

 is ready for their reception. Thanks to this diHgcnce, 

 therefore, pollen is brought to the pistils, as soon as they 

 are ready for it, by the ** fastest snail-express." 



