54 



This experiment with hyacinth broth was repeated, inoculating a 

 tube of the same stock with a moderate-sized loop from an alkaline 

 beef -broth culture 12 days old, i. e., with more germs. All the other 

 conditions were the same. 



Besult. — The first trace of growth was on the fifteenth day. On 

 the nineteenth day there were distinct rolling clouds and a yellow rim, 

 but no precipitate. Subsequently there was a copious growth and a 

 ver}' heavy precipitate. No crystals formed. 



Ps. jjhaseoU and Ps. campestris both grew in this fluid, the latter 

 much more readily than the hyacinth germ. 



The discover}^ of this sensitiveness to acids furnished a satisfactory 

 explanation of some perplexing contradictions obtained with unneu- 

 tralized beef, potato, and cauliflower broths earh' in my stud}- of Ps. 

 hyacintM. It also afforded a partial explanation of the slow progress 

 of the disease in the host plant, but apparently not a full one, since 

 once well established in the vessels, it is not clear why the parasite 

 does not immediately advance into and destro}^ the acid parench^^ma 

 under cover of the alkalies which it produces. Evidently there are 

 additional difficulties to be overcome, one of which will be discussed 

 in the following section. 



FEEBLE DIASTASIC ACTION. 



The meager development on cooked potato led to the belief that 

 something in this substratum inhibited the growth of the hyacinth 

 organism. In the beginning it was thought that the feeble growth 

 might be confined to certain varieties of potatoes and that on others a 

 better growth could be obtained. To test this, cultures were made on a 

 variety of tubers, new and old. but with the same result. Subsequenth' 

 tubers were procured from a variety of soils and from climates as 

 different as New York and Florida, but there was little difference in 

 the amount of growth. The growth was comparativelv feeble no 

 matter what the age or origin of the potato. It was then thought 

 that possibly the acidit}^ of the potato might be the restraining cause, 

 and dilute caustic soda was added to potato cylinders, so as to I'ender 

 them neutral or feebly alkaline after they were steamed. On such 

 cylinders the organism grew little if any better than on the untreated 

 potatoes (41 days), and this h3^pothesis was also abandoned. I then 

 began to suspect that the feeble growth was wholly a matter of insuffi- 

 cient nutrition, and found that on adding considerable quantities of 

 cane sugar the growth increased rapidh^ and became very abundant. 

 About the same time tests with iodine showed that the starch of the 

 potato, even close under the bacterial layer, had been very little acted 

 upon b}^ the organism. 



The rather meager growth of this germ on potato now appears to me 

 attributable to its feeble diastasic action, i. e., to its inabilit}- to get 



