I 2 



proper development. This trouble begins to appear after the plants 

 have become well established in the permanent bed. Affected spec- 

 imens show at the summit or growing tip a light greenish-yellow 

 color instead of the normal dark green. Leaves previously formed 

 do not change their color, but from the point where the trouble 

 began the succeeding stem and leaves have the yellow color. There 

 is no dying or any such effect, simply the "spindling" yellow 

 growth. The effect is curious and unmistakable. At the same time 

 similar yellow shoots begin to appear from the axils of the leaves on 

 the main stem. In the worst cases growth is checked at this point 

 and the plant remains through the summer as shown in fig. 6, a 

 stunted stem, yellow at the top, with numerous short, unhealthy- 

 looking yellow branches along the sides. From this the intensity of 

 the trouble varies to the other extreme where only in a few of the 

 last flowers of the season is the abnormal color and growth apparent. 

 Microscopic examination of the affected stem and leaves shows 

 nothing abnormal except a lack of green coloring matter. The roots 

 even of the most diseased specimens are abundant, sound, and 

 healthy-looking (see fig. 6). Absolutely nothing has been found in 

 any part of the plant to account for the effect. After the disease 

 once appears it keeps cropping out here and there all through the 

 season, the latest plants to show it being the least affected. The 

 most striking effect of this peculiar malady is seen in the flower. 

 The Jlower^ so-called, of the aster, is, it should be remembered, in 

 reality a large number of very small flowers crowded together upon a 

 disk-like base or receptacle. Two forms of these small flowers or 

 florets occur, those about the edge, the ray florets, each of which 

 bears a single petal, and those in the center, the disc florets. This 

 is seen most plainly in the single aster, where the disc florets form 

 the yellow center or " eye " of the flower. The double-flowered 

 forms, which are considered most desirable, are the result of the 

 transformation of the disc florets into ray florets, so that each bears 

 a petal. The more complete this transformation the more double 

 the flower. A perfectly double aster is not common except in certain 

 varieties, for the center usually remains in its normal form. The 

 disc florets bear both stamens and pistils and so always produce 

 seed. The ray florets bear only pistils : consequently they produce 

 no seed unless fertilized with pollen from the disc florets. For this 

 reason the well-known fact conies about that the more double the 



