88 



SCIENCE 



[X. S. Vol. XXVI. No. 655 



is an active parasite attacking the twigs, limbs 

 and trunk of the peach, plum, apricot and 

 cherry trees. 



On the peach, infection occurs through the 

 buds and wounds at any time during the 

 growing season, but its development is most 

 noticeable during the spring months. Alter- 

 nating freezing and warm periods during late 

 winter appear to bring about favorable con- 

 ditions for the growth of this organism. It 

 often makes considerable advancement during 

 the warm weather in winter. The young 

 shoots are frequently killed back from two to 

 fifteen inches during the months of Janu- 

 ary and February. As many as three hun- 

 dred diseased twigs have been counted on a 

 single tree. Twigs killed during the winter 

 months at first have a dark purplish skin, 

 but later the skin on the infected areas be- 

 comes leathery and shades into scarlet and 

 purple, giving the twigs a characteristic ap- 

 pearance. The leathery colored areas finally 

 change to drab, and the skin on the diseased 

 tissue becomes loose and wrinkled. Black 

 fruiting bodies (Cytospora ruhescens Nit- 

 schke) soon appear below the epidermis on the 

 drab-colored areas. These bodies gradually 

 enlarge and push a white disk-like cap 

 through a transvei-se slit in the epidermis. 

 The entire dead portion of the twig gradually 

 changes to drab in color and becomes more or 

 less dotted with the black silvery capped 

 pustules. During wet weather these black 

 Cytospora bodies push out very fine red 

 threads which are composed of masses of 

 spores. These spores are soon scattered by 

 the rain and insects and start new points of 

 infection. 



The diseased portion of the twig soon be- 

 comes constricted, making the division be- 

 tween the dead and living tissue very marked. 

 Gum pockets also form at this point, which 

 frequently rupture the epidermis and pro- 

 duce a copious gum flow. 



During the spring and summer months the 

 foliage of infected twigs frequently wilts sud- 

 denly and takes on a brown blighted appear- 

 ance. This blighting is due to the fungus 

 girdling the stem. A gradual killing back 



also occurs, but the injury in such case is 

 not so noticeable. 



Infectious on the older branches during 

 the winter and early spring raonths pro- 

 duce oblong wounds extending up and down 

 the stem. The epidermis covering such 

 wounds cracks and falls away exposing the 

 wood. Callus soon pushes out from the edge 

 of the injury and finally covers over the 

 exposed tissue. The lips of the newly-formed 

 bark, when they meet, do not unite and often 

 leave a slit or opening through which gum 

 exudes. Injuries of this sort finally produce 

 slightly elevated, oval-shaped scars on the 

 branch, and it is not uncommon to find from 

 fifteen to twenty wounds and scars on a limb 

 five or six feet long. In the more severe 

 cases there is constantly an enlargement of 

 branch about the point of injury, frequently 

 producing rough, black barrel-shaped enlarge- 

 ments. 



On the larger limbs and trunk, especially 

 on the southwest side, large cankers or so- 

 called sun scald wounds are formed. Such 

 injuries are gradually extended, often girdling 

 the limbs and even the trunk of the tree. 

 The gumming is also constantly associated 

 with these cankers. 



Large limbs or even whole trees in different 

 states of vegetation and at different times of 

 the year die suddenly. The foliage of limbs 

 or trees which die late in the spring and sum- 

 mer takes on an unhealthy, starved appear- 

 ance and wilts suddenly and shrivels. The 

 leaves of those that will die during the fol- 

 lowing winter in most cases also take on a 

 yellowish color and fall prematurely. 



On the infected areas of the limbs and 

 trunk Cytospora- ruhescens Nitschke and Valsa 

 leucostoma Pers. usually develop. Inocula- 

 tions made with pure cultures of Yalsa leucos- 

 toma on peach and plum trees produced 

 wounds on which Cytospora ruhescens in- 

 variably developed. Spores of Yalsa leucos- 

 toma placed on sterilized peach twigs also 

 produced Cytospora ruhescens. Inoculations 

 made with pure cultures of Cytospora ruhe- 

 scens on peach and plum trees produced 

 wounds on which Cytospora ruhescens con- 

 stantly developed. Cytospora ruhescens 



i 



4 



