444 



BOTANY OF THE LIVING PLANT 



surface. This stage was first described as " Cluster-Cup^," and 

 regarded as a distinct fungal disease under the name of Aecidium 

 berberidis (Fig. 376). But it is now known that the spores produced 

 by the cups are able on germination to cause a new infection of the 



Fig. 377- 

 Longitudinal section of a leaf of Wheat, sliowing a tuft of Uredo-spores bursting 

 tlnrough tfie epidermis. Highly magnified, (.\fter ]\farshall Ward.) 



leaves of the Wheat plant, which results again in the growth of a 

 mycelium bearing the uredo-spores. There are thus two stages 

 of the disease, the one on the Wheat or other Grasses, the other 

 on the Barberry. Long before it was proved that these two different- 

 looking diseases were only stages in one life-history, a connection 

 between the two had been suspected. It was thought that the 



I-IG. 37S. 

 Germinating Uredo-sporcs, showing various stages of de%'elopment of the germ- 

 tubes, a, /', ... Very highly magnified. {After Marshall Ward.) 



Barberry was in some way injurious to Wheat. But it was not till 

 late in the nineteenth century that tlie cycle was completely demon- 

 strated. A similar heteroecismal life is now known for about tiftv 

 species of Rusts. One of the commonest is Piicn'iiia civid's, of whii'li 



