WATER RELATIONS OF OTHER SPECIES 149 



relation with water load, ascertained either by weight or analyzed 

 water content. It is known, for example, that maize (Maximow, 

 '29, p. 210), wheat (Vassiliev, '36), and many other species 

 (Knight, '17; Pisek and Berger, '38) readily suffer reductions of 

 water content, and that evaporative losses are then diminished. 

 Gain by intake through roots as soon as water again becomes avail- 

 able is presumably faster than in controls. Rates of turnover are 

 often enormous, some plants exchanging their own weight of water 

 every hour (Knight, '17). In aquatic plants with large fronds, 

 half of recovery from desiccation occurs in a few seconds (Kalt- 

 wasser, '38). 



It is, however, not proposed to analyze further any of the data 

 concerning organisms that are ordinarily considered to belong to 

 the plant kingdom. 



§ 56. Summary 



Of the many kinds of animals whose maintenances of water con- 

 tent might be studied, a small sample is available for future com- 

 parisons. Only two species of invertebrates (Lumhricus and Zoo- 

 thamnium) having turnovers, were examined for rates of exchange 

 during recovery from both excesses and deficits. Both are as well 

 equipped to correct water contents as any mammal. 



No turnover of water and no special structures for water ex- 

 changes are found in some animals that live in sea water. In water 

 balance any possible turnover is then by the imperceptible replace- 

 ment of molecule for molecule. In water increments, adjustments 

 still result in an equilibration. 



No species has been found without augmentations in rates of the 

 appropriate net exchanges, whenever water loads occur. This fact 

 strengthens the impression that the maintenance of water content 

 in any species may be universally studied by correlating rates of 

 net water exchanges with water loads. 



Very often ''water diuresis" is considered a wide-spread phe- 

 nomenon. Extending the term to include all increases in rate of 

 water output by any visible path when positive water increments 

 prevail, actually I find data demonstrating it in 8 species of mam- 

 mals, one species of birds (Burgess et al., '33; Korr, '39) four of 

 reptiles (fig. 80; Burgess et al.; Boyd and Dingwall, '39; Friedlich 

 et al., '40), one genus of amphibia, one species of fishes (see fig. 

 102) ; two species of insects (fig. 84; Lester and Lloyd, '28), one 



