THE AMERICAN BOTANIST 81 



wliich were so arranged that no matter how thrown on the 

 ground one or more spikes projected upward to bother pursu- 

 ing horsemen when an army was in retreat. Tlie Latin name 

 for this implement was fribulus which suggests some of the 

 tribulation it must have caused and has appropriately been 

 taken as the name of the genus. A further and better illustra- 

 tion of the use of the name, tribulus. is found in the specific 

 name for the sand bur (Cenclirus tribuhi'Jcs) . The well- 

 known fruit of this species is a miniature tribulus and to this 

 day bothers the barefoot boy much more than the contrivance 

 for which it was named ever could have troubled the tribes 

 which warred on Rome. 



Double Sunflowers. — Two separate and distinct ideas 

 are embodied in our conception of double flow'ers. In the 

 commoner instance a double flower contains more than the us- 

 ual number of petals due either to the transformation of sta- 

 mens or of some other part, or to the splitting of the initial 

 mass of cells designed to become a petal. It would, however, 

 be just as rational to call a flower with more than the usu'd 

 number of stamens a double flower, the point is that some or- 

 gan of the flower has been multiplied. This however, is not 

 true of the second phase of what we call doubling and which is 

 well illustrated by double daisies, double sunflowers and the 

 like. Here no additional parts are found. Such doubling con- 

 sists simply in a more luxuriant development of isome of the 

 corollas in the flower head. The flowers mentioned all have 

 ligulate corollas in the outer circles and our doubling is simply 

 due to the fact that more of the regular corollas have become 

 irregular and ligulate. If this is really doubling, the dandelion 

 is one of the best naturally double ''flowers" we have. The 

 cause of the increase and change in the corollas of composite 

 flowers is not easy to discover. The parent of the well-known 

 garden plant "golden glow" grows along thousands of miles of 

 streams and in countless swanips, and shows little tendency to 



