H. AVOKMALD 49 



To supplement Experiment 2 another experiment was carried out at 

 the same time in which one plum of a cluster of five was inoculated at a 

 puncture. The disease extended rapidly through the plum primarily- 

 infected, then from that* to the two in contact with it and from those to 

 the remaining two so that eventually all five were affected. The result as 

 seen on July 21 is shown in Pi. IX, Fig. 6, the plum in the middle being 

 the one inoculated through a puncture on June 26. 



It is evident therefore that the twigs affected with the " Wither Tip" 

 disease are a source of danger to the fruit, for although wounds are 

 necessary to enable the fungus to gain an entrance in the first place, ob- 

 servation has shown that injuries severe enough to rupture the skin are 

 not infrequent; bruises and abrasions occur dujing storms and biting 

 insects pierce the skin and leave open wounds. 



{d) Inoculation of Apple Flowers. 



Since the strain of Monilia cinerea obtained from the plum twig and 

 used in the experiments described in the preceding pages was morpho- 

 logically similar to the form which produces the "Blossom Wilt and 

 Canker" disease of apple trees it was to be expected that it too was 

 callable of producing the "Blossom Wilt" when inoculated into apple 

 flowers, although it is to be observed that the particular strain used in 

 the experiments on plum flowers and fruit could be distinguished in 

 cullure from that which so readily infects the flowers of the apple, in 

 that the former remains hyaline^ in agar cultures containing prune juice 

 while the latter always produces a dark brown coloration when growing 

 on that medium. Experiments were therefore carried out to ascertain 

 whether this hyaline strain from the plum could attack the flowers and 

 spurs of the apple. 



Experiment 1. 



Young trees of the Worcester Pearmain variety growing in pots were 

 used. A similar experiment on this variety carried out in 1917 but 

 using a strain obtained from a Monilia canker of an apple tree resulted 

 in the typical blossom wilt condition in two out of six flowers inoculated. 

 In the present experiment, using the hyaline strain employed in inocu- 

 lating the plum flowers and fruit, seven flowers were inoculated, viz., the 

 central flower of each of seven umbels. Newly opened flowers (i.e. those 



1 One tube culture of this strain did give rise to irregularly distributed brownish patches 

 but even then it was easily distinguished from the much darker cultures of the various 

 strains obtained from apple trees. 



Ann, Biol, v 4 



