134 The Nature-Study Idea 



tect it from its enemies? The teacher may as 

 well have said that Jimmie Brown has freckles 

 so that the sun will not tan his skin; and the 

 statement would be hard to disprove. 



A teacher asked me whether it is not true 

 that her cactus has spines in order to protect 

 it from browsing animals. I told her that I 

 did not know. As I was a stranger to her, she 

 wondered at my ignorance. She wanted to 

 know why I did not know. I told her that I had 

 no good evidence that an animal ever wanted to 

 browse on her cactus or its ancestors. Perhaps 

 the cactus spines are older than the browsing 

 animals. Perhaps there was some special con- 

 dition or reason in geologic time. Perhaps the 

 spines were in some way an incidental result 

 of the contraction of the plant body, which con- 

 traction was associated with the necessity of 

 reducing the evaporating surface in an arid 

 climate. Perhaps a hundred things. She was 

 surprised that I had to go into geologic time 

 to bury my ignorance. She wanted cause and 

 effect side by side, and in the present. Then 



