THE AMERICAN BOTANIST 



147 



''Columbian Cyclopedia" says "the cacti are without exception, 

 natives of America." In the face of such contradictory opinions 

 from what we are used to consider authorities, we hesitate to 

 decide. That there are cacti growing without cultivation in 

 various parts of the Old World is not questioned, but whether 

 these are native species or merely American species that have 

 become naturalized is the question. On the other side of the 

 world certain other species, notably the spurges, take on the 

 appearance of cacti, but such forms would scarcely be mistaken 

 for cacti by scientific men. If any of our readers can settle this 

 question we would be glad, if they would furnish the names of 

 such foreign species and data as to the country they inhabit. 



Ultra- Violet Flowers. — The rays of visible light, as 

 everybody knows, forms but a small fraction of the number 

 Avith which the physicist is familiar. The human eye perceives 

 only those rays which produce the color sensations which we 

 know as red, orange, yellow, green, blue, indigo and violet, but 

 man has made a sort of artificial eye — the photographic plate — 

 which has a much wider rang"e and can perceive rays beyond 

 the red end of the spectrum as well as others beyond the violet 

 end. As may be supposed, there is a great difference in the ap- 

 pearance of objects photographed first by ordinary light and 

 then by ultra-violet light. If objects absorb the ultra-violet 

 rays, they come out dark on the photographic plate, while if 

 they have the power to reflect the rays, they come out nearly 

 white. TwO' Costa Rican experimenters have been examining* 

 a great many different flowers in ultra-violet lig"ht with the 

 result that they have found about a dozen which reflect so much 

 of this light that they propose to name them ultra-violet 

 flowers. All corollas thus far found which have the power of 

 reflecting the ultra-violet rays are yellow, and among them are 

 the dandelion, pumpkin, cucumber, sow thistle and evening- 

 primrose. The investigators whose notes appear in the Scien- 



