i6 



Beside these changes it may be mentioned that plants which are 

 at all affected bear little or no seed, even in the normal flowers. 



Consideration of these changes, together with the general study 

 and observation of the disease, leads to the conclusion that they (the 

 changes in the flower particularly) are not the direct effect of the 

 cause of the trouble, whatever it may be, but are simply secondary 

 symptoms of a certain weakness. They all indicate plainly a rever- 

 sion from the reproductive to the vegetative function. The elonga- 

 tion of the pistil, the abortion of the stamens, the transformation of 

 the pappus hairs into green lobes, the strong response of the affected 

 florets to the effect of gravity, and the non-production of seed, all 

 go to show, not that the flower is diseased, but that from some cause 

 the plant lacks the vitality or form of vitality necessary for the 

 reproductive function. A strikingly suggestive similar case helps 

 out this idea. Marguerite plants in our college greenhouses have 

 recently shown a disease very closely resembling this of the aster. 

 The same yellow shoots appear and the same effects in the flower 

 (fig. 17). Here, however, it occasionally occurs that a form such as 

 is shown in fig. 18 develops. Here each pistil has elongated into a 

 stem, bearing another flower bud, so that the single blossom would 

 become, if all expanded, an umbel-like cluster of flowers. These 

 secondary buds, however, have never been known to open into 

 flowers. Here, then, the change from the reproductive to the vege- 

 tative is still more plainly brought out. Besides in the Marguerite, 

 it may be mentioned that similar diseases to that of the aster have 

 been observed in the Calendula and African Marigold, each produc- 

 ing the yellow spindling shoots and abortive flowers. Plants of the 

 ragweed or Roman wormwood (^Artemisia) are also often seen in this 

 vicinity which show a yellow color and quite similar appearance. 



CAUSE OF THE YELLOW BLIGHT. 



A number of different causes have been assigned to this disease 



by aster growers. First may be mentioned the case described by 



Dr. W. C. Sturgis of the Connecticut Experiment Station, who 



ascribes what appears to be this same disease to the 



Nematode effects of Nematode worms on the roots. Nothing 



Worms. is said about the peculiar effect in the flower, but the 



spindling yellow growth is mentioned. While it is 



not improbable that the root-gall nematode might attack this plant 



