126 MISSOURI BOTANICAL GARDEN. 



ammonium carbonate, five days after the spraying. It 

 will be noted that the entire lower surface of the leaf is 

 covered with isolated raised warts, which are irregularly 

 scattered over the entire surface of the leaf. These warts 



are shown somewhat enlarged on plate 26. They form 

 more or less circular, raised knobs of a yellowish color, 

 growing lighter as they grow older, and, after ten days or 

 two weeks, becoming almost white. The individual warts 

 are well defined, rising immediately from the surface of 

 the leaf in a sharply defined circle. Many of the warts 

 grew to a very large size, projecting out from the surface 

 of the leaf, in some cases for one-eighth of an inch. 



In the early stages the warts appear as small swellings 

 of the epidermis ; the latter, however, was soon broken, 

 or, more correctly, was lifted up on the surface of the 

 growing wart. After six or seven days, a distinct star- 

 like appearance developed under the larger warts. There 



appeared to be a more or less central body from which 

 lines extended out in a radial direction, giving the appear- 

 ance of a star-shaped wreath around a central solid body. 

 Reference to plate 26 will show many of the bodies in this 

 condition. At this period the warts were almost uni- 

 formly white in color. From the period of this star-like 

 structure, the growth evidently ceased and after several 

 weeks the warts gradually dried up, so that after three 

 weeks or thereabouts they had practically shriveled up. 

 Although both surfaces of the leaves were sprayed, the l 

 warts appeared almost entirely on the lower surface of the 

 leaves. 



A microscopic examination of the healthy cauliflower 

 leaves shows a well-defined spongy parenchyma layer on 

 the lower surface of the leaves, and a palisade parenchyma, 

 composed of several rows of more or less rectangular cells 

 (plate 27, fig. 1). Sections made through the early 

 stages of the swellings (plate 27, fig. 2) show some of 

 the spongy parenchyma cells enlarged to many times their 







