FRUIT OF POLAR BEAR CACTUS 



'J'he fruit of Opuulia floccosa is here shown, natural size. It 

 will be noted that while the plant is strongly protected 

 by spines and hairs, the fruit is quite naked. Possibly 

 this is to make it edible for animals and thereby promote 

 the distribution of the seeds. The naked fruit is also 

 Isetter adapted to rolling down hill, and thereby spread- 

 ing its seeds, than a spiny, hairy, fruit would be. 

 (Fig. 7.) 



at an altitude of 4,500 meters, nearly 

 15,000 feet. » 



One of the difficulties attending the 

 study of adaptation is that of determin- 

 ing definitely the tise of the s])ecialized 

 fcattire. Interpreting the uses of ]:)ecu- 

 liar characters is a fertile field of 

 speculation, as the history of the subject 

 abundantly shows. Appearances are 

 often very deceptive or, at least, have 

 often proved very misleading. Finding 

 a cactus with a shaggy coat on the bleak 

 tablelands exposed to nightly frosts in 

 winter has naturally suggested that the 

 hairy covering is a protection against 

 cold, ])ut the fact may be quite the 

 opposite. In the rare atmosjihere of 

 the highlands the siui has a scorching 

 pfjwer that is i:)robal)ly much more 

 trying to the plant than the cold. ICven 

 at temperatures above freezing, plants 



are often killed by too sudden exposure 

 to the sun after a cold night, while those 

 in shady situations survive. With stems 

 and roots chilled, the demands of rapid 

 transjjiration cannot be met and the 

 heated tissues collapse. 



PROTECTION FROM THE SUN 



With such facts taken into account it 

 is easy to understand that a coat of hairs 

 may be even more useful to keep the 

 plants from warming up too suddenh- 

 than to be a ])rotection against cold. 

 The cooling of the i)lant may be some- 

 what retarded by the hairs, Init this 

 can hardly \)0 of as much imjjortance 

 as the protection assured by the hairs 

 against the injurious effects of sudden 

 exjjosure to the heat of the morning sun. 

 The practical bearing of this idea has 

 been recognized by fruit growers who 



' Webcrbauer, .\., I'Ml, Die I'danzinwcll dcr Pcruanischen Andcn, p. 195, pi. \S. 

 118 



