02 A Phj/tophfhora Bot of Pears ami Apples 



were fewer in number and sexual organs were present. The affected 

 internal tissues were found to be permeated with the non-septate 

 mycelium. A small portion of a section, made with a stsrilized razor 

 through the infected flesh of one of the pears at 0-5 cm. below the sur- 

 face, was placed on agar and gave rise to a culture similar, in general 

 appearance and in the production of sexual organs, to those cultures 

 obtained from sporangia. 



Inoculation Experiment 4. On August 9, 1913, an experiment was 

 carried out on pears growing in the open. Five were inoculated by 

 making a w^ound through the skin and inserting mycelium from a pure 

 culture growing on agar. Two pears w-ere similarly wounded but sterile 

 agar was placed in the wounds. A fortnight later one of the pears inocu- 

 lated with mycelium was found on the ground and tw^o others fell at a 

 touch while under examination ; the rest, including the controls, remained 

 on the tree uninfected until ripe. 



The pear found on the ground had been attacked by another fungus, 

 for on keeping it in a damp chamber no fructifications appeared and 

 a particle of the flesh placed on agar gave rise to growth unlike that of 

 the Phytophthora. The other two infected pears, however, produced 

 numerous sporangia on being kept for a few days in a damp chamber. 



Two of the five pears inoculated with mycelium had therefore be- 

 come affected with the Phytophthora rot. 



Inoculation Experiment 5. In the following year an experiment was 

 carried out on young pear trees growing in pots in the greenhouse. On 

 September 10 eight pears were inoculated (four of each of the varieties 

 Fondante d'Automne and Doyenne du Comice) with mycelium from a 

 pure culture as in the preceding experiment, and on the opposite side of 

 each pear a control wound (not inoculated) was made. At the end of 

 six days five of the pears showed a blackened area 1-5 cm. in diameter 

 round the inoculated wound and in a fortnight from the beginning of the 

 experiment the rot had made distinct progress in all, half the surface 

 in six of the pears being affected and about one quarter of the surface 

 in the other two. On the control side of each no rot occurred at the 

 wound except in one case in which a soft rot caused by a Botrytis made 

 its appearance. 



Under the conditions which obtained in the greenhouse no sporangia 

 were seen at this stage, the atmosphere probably being too dry, so three 

 of the infected pears (including the one with Botrytis) were cut off and 

 placed in damp chambers: Phytophthora sporangia developed, on the 

 side inoculated, in each case within a few days. Of the five remaining, 



