72 TEXTBOOK OF BOTANY 



If the removal of cedars is out of the question, the disease 

 can be greatly checked by spraying the apple trees at the 

 proper times with Bordeaux mixture. It may be largely 

 avoided also by planting resistant varieties of apple ; but un- 

 fortunately some of the most valuable varieties are very 

 susceptible to the rust. 



101. Some Other Rusts. The blister rust of the pine, until re- 

 cently known only in Europe, passes its summer stage and forms 

 summer and winter spores upon currants and gooseberries, sometimes 

 seriously injuring these hosts ; its spring stage causes a very destruc- 

 tive disease of the white pine. This rust has lately been found in 

 North America, and it is not unlikely that it will greatly interfere with 

 the future raising, of white pine for forestry purposes. The fungus 

 may live for years in the bark of the pine. Its winter spores differ 

 from those of the wheat rust in being only one-celled. The rose rusts, 

 differently from the rusts so far mentioned, pass their whole life upon 

 a single host plant. Their spring spores are borne in irregular son 

 rather than in cups, and each winter spore consists of a row of several 

 cells. Some varieties of roses are badly injured by these rusts. The 

 common orange leaf rust of raspberries and blackberries produces 

 both spring and winter spores upon the same host ; it has no summer 

 spores. The asparagus rust also has no summer spores ; it forms its 

 spring and winter spores on the asparagus. The life cycle of the rust 

 of mallows and hollyhocks is very short. It has nothing that corre- 

 sponds to the spring stage of the wheat rust, and no spring spores, 

 spermatia, or summer spores. Spores are formed that correspond to 

 the winter spores of the wheat rust. Some rusts, living from year to 

 year in the tissues of certain trees, stimulate the host plant to the 

 very rapid production of branches in the infected part, and so cause 

 the formation of a " witches' broom." Such " brooms " are produced 

 on the red cedar by relatives of the apple rust. 



102. Historical Note. The notion that the presence of barberries 

 is in some way harmful to growing wheat was prevalent in Europe as 

 early as the middle of the seventeenth century. It is said that the 

 parliament of Rouen in 1660 ordered the destruction of barberries. 

 Similar laws were adopted in Massachusetts in 1755, in Lippe in 1805, 

 and in Bremen in 1815. Experiments carried on in the latter part of 

 the eighteenth century and the early part of the nineteenth in England, 

 Denmark, and Germany indicated that barberries are in some way 

 responsible for the occurrence of the wheat disease which was then 



