14 



The normal development of an aster blossom is seen in fig. 8. At 

 the end of each shoot there first appears a cluster of small, leafy 

 bracts, from the center of which the flower bud gradually develops 

 and opens. In plants badly affected with the yellow disease no 

 flowers develop upon the yellow sickly-looking shoots, or only rudi- 

 ments of them. In numerous cases, however, blossoms appear upon 

 normal branches, which are peculiarly afifected by the disease. 

 Some show it in the whole flower, others only upon one side or in a 

 small portion. The first noticeable peculiarity is in the color, which 

 is of the same greenish yellow as that of affected leaves, without 

 regard to the natural color of the variety. Where the whole flower- 

 head is affected it has a peculiar unnatural appearance, while often 

 one side is perfectly normal while the other is yellow and diseased. 

 (Fig. 9.) Closer examination of affected florets shows a remarkable 

 and characteristic change. This is the greatly increased size and 

 length of the pistil, which occupies the center of each floret. 

 Fig. 10 shows a normal and a diseased floret, all the parts being 

 removed except the pistil. These are drawn to the same scale. 

 The ovary or seed-bearing part at the base is much longer and 



Fig. 13. Later stage of Fig. 12. (^dis- 

 eased, « normal. 



Fig. 15. Portions of pappus hairs, ix nor- 

 mal ; /' modified form found in Yellow Disease. 



