84 THE AMERICAN BOTANIST 



best nourished plants. In the flowerless plants, also the best 

 nourished plans are always female. Cases are rare, however, 

 in which the sex, once fixed, may be changed by subsequent 

 manipulation though there is some evidence of it in the south- 

 'ern pawpaw (Carica). 



Color Changes in Flowers. — It is sometimes difficult 

 for the non-botanical to understand how a single substance 

 can produce a variety of colors. For instance, carotin, the 

 substance that gives the carrot its color, is also responsible for 

 the color in many yellow, orange, red and black fruits and 

 flowers. The colors of flowers seem due to comparatively few 

 pigments chemically combined with other elements. A re- 

 cent study of the colors of the bee-balms (Monarda) indicates 

 that a single substance called thymoquinone, may cause all 

 the variations noted in the flowers, the different shades being 

 due to various degrees of oxidation. Most plants contain 

 oxidizing ferments called oxidases which bring such color 

 changes about. In some cases colorless substances in the plant 

 may become colored when combined with oxygen. The 

 oxidases are usually easily destroyed by heat behaving as most 

 plant ferments do under such circumstances. 



Herbaceous Grounds. — In the newer botanical gardens 

 it is sometimes the custom to arrange the herbaceous plants 

 by themselves thus separating them from their allies among 

 shrubs and trees. Concerning this, James MacPherson a well 

 known gardener of Trenton, N. J. writes: "Bernard de Jus- 

 sieu, the uncle of Antoine, laid down a succession of natural 

 groups at the "Jardin Royal de Trianon" during the years 

 1750-1759. He was the first man to base his work upon sound 

 philosophical rules and his nephew Antoine de Jussieu did 

 much to enlarge upon and complete his system in his "Genera 

 Plantarum" of 1789. He went far to prove that the arrange- 

 ment by the famous Bernard de Jussieu was sufficient for the 

 classification of vegetation in seven main divisions, and it 



