1893.] NATURAL SCIENCES OF PHILADELPHIA. 307 



green-surfaced leaves seem on wholly different plants. The latter 

 has undulate, and occasionally crenate serrate, leaves ; and the leaves 

 are minutely dotted in places where hair should have grown. 



Endurance of Portulaca oleracea. 



In early autumn light white frosts occur, the tenderer plants 

 being injured in patches. Blackened leaves occur at intervals, 

 and considerable areas will have escaped, though of the same 

 species as those injured. This erratic character of an early light 

 frost is usually referred to atmospheric currents, the atmosphere 

 being a trifle higher or lower according as injury or escape from 

 injury may result. This is probably the case, though no absolute 

 tests by self registering thermometers have been made to my knowl- 

 edge. 



After one of these early frosts, the past October, I noted that a 

 large area covered with Portulaca oleracea, the common Purslane, 

 had a large number blackened by frost, while possibly an equal 

 number were- unharmed. I was about passing over the fact under 

 the explanation already noted, when I observed that in many 

 instances healthy plants and plants blackened by frost would be 

 found together, their branches interlacing. In every case of the 

 kind examined, not a single leaf would be injured in the one case, 

 while in the other case the whole plant would be destroyed. The 

 destruction in these cases could not have been by any variation in 

 the intensity of the cold wave, but must have been from a less 

 power of resistance in the plant itself. 



The facts detailed furnish valuable lessons and suggestions. May 

 not the varying effects of a first " white frost " be as often from 

 varying powers of resistance as from varying intensities of the cold 

 wave? 



Again it is frequent to have increased hardiness, as well as many 

 other characteristics, referred to the effects of environment. As the 

 plants here, and their ancestors for many generations, must have 

 been under like conditions, the unequal results can scarcely be 

 attributed to environment, but to the elasticity of character pos- 

 sessed by the whole organized world. In Portulaca oleracea we may 

 safely say some plants are hardier than others ; yet over the whole 

 northern world where it is found, the plants are yet totally destroyed 

 by a comparatively light frost. Ages of existence under severe 

 climatic conditions have not rendered it, on the whole, hardier than 



