(4^3)" 



There are, however, some species which are more injurious to the 

 cedars than those which have their aecia on economic aecial hosts. 

 G. Betheli, common on Juniperus scopulorum in the Rocky Moun- 

 tains, is one of the most destructive species known. The white 

 cedar (Chamaecyparis thyoides) is attacked by two species, G. 

 Botryapites (G. biseptatum) and G. Ellisii, the former producing 

 swellings of the trunk and branches and the latter witches' brooms, 

 both often threatening the welfare of the trees. 



Control 

 Methods for the control of these, as well as most other rust-dis- 

 eases are as yet uncertain or impracticable. Segregation of the mem- 

 bers of the apple and cedars families will accomplish the result but 

 is not always possible. In making new plantings, however, this 

 suggestion is worthy of consideration on the part of farmers, or- 

 chardists, and landscape gardeners. Spraying as recommended 

 for other fungous diseases has been tried with incomplete success 

 by many different workers. Attempts have been made (i) to 

 prevent teliospore germination by spraying the cedar when the 

 spore-masses were expanded; (2) to prevent infection of the apple 

 by basidiospores (sporidia) by spraying the apple trees just after 

 teliospore germination (i. e., after a rain); and (3) to prevent re- 

 infection of the cedars by spraying them to inhibit aeciospore 

 germination on them when the aeciospores are being distributed 

 in the late summer (see Heald, 1909). Variable results seem to be 

 obtainable depending upon the nature of the season and the judg- 

 ment of the operator. The first two schemes are open to practical 

 objection not only because spraying is necessitated after every 

 rain for a considerable period in the spring but also because a 

 delay of a few hours after the rain is sufficient to make the spraying 

 useless. The third scheme is apparently an impossibility because 

 of the long period during which spores are being discharged and 

 the lack of any climatic conditions to indicate when distribution 

 is going on. Another suggestion which has been made for the 

 benefit of orchardists concerns the resistance of the varieties 

 grown. This is without doubt deserving of attention as it has 

 been shown (Stevens and Hall, 1910; Stewart, 1910; Lloyd & 

 Ridgway, 1911) that the varieties of apples and pears differ very 

 greatly in their susceptibility. This suggestion may not be so 

 easily followed in practice, however, because the resistant qualities 



