76 THE BIOLOGY OF FLOWERING PLANTS 



Egyptian desert, and describes simple absorbing hairs from 

 species of Diplotaxis and Heliotropium. Haberlandt has 

 found absorbing hairs on other plants, e.g. Centaiirea 

 argeyitea. Volkens also supposes that the saline incrusta- 

 tions of the glands of various desert plants condense water 

 at night, and that this water is utilised by the plant. The 

 salts certainly deliquesce at night, but, as the plant would 

 require to develop an osmotic pressure of about 400 atmo- 

 spheres to withdraw the water, and as such pressures are 

 quite unknown even in desert plants, it does not seem 

 likely that this can be a source of water supply. 



The hairs which grow in little bunches in the angles of 

 the veins of many European trees, and such hairs as those 

 which form a line on the stems of the chickweed, have been 

 supposed by Lundstrom (1884) to function in absorbing 

 rain or dew. Whether they really have any importance in 

 this respect must be very doubtful. It is true, however, 

 that the leaves of many broad-leaved trees do take up water 

 quite readily. If the leaves of one branch of a forked twig 

 of beech be immersed in water, those of the exposed branch 

 remain turgid for some days ; water is therefore absorbed 

 and transported in sufficient quantity to replace that lost 

 by transpiration. It is possible that this faculty of absorp- 

 tion may be of some importance to a plant in enabling it to 

 restore its turgor rapidly in rain, or dew, after a drought. 

 That any plants can actually condense and utilise 

 atmospheric moisture seems doubtful (cp. Wille, 1884). 



Summing up, we may say that rain and dew are of 

 extreme importance to many epiphytes which possess 

 specialised absorbing organs ; and that rain and dew may 

 occasionally be utihsed by ordinary plants. 



The Bladderworts. — Finally, we may mention the 

 case of the terrestrial and epiphytic bladderworts. Cha- 

 racteristically these insectivores have a submerged vegetative 

 system. Gliick (1905) has described land forms of most of 

 the common species, and Goebel (1893) has fully investigated 

 several American species which habitually live in moss 

 and epiphytically. Thus Utriciilaria neliimbifolia and U. 



