﻿Grossenbacher: Medullary spots and their cause 231 



found in their channels mining their way out above the ground 

 during the early forenoon of May 21. Again late in the afternoon 

 some were found with their heads protruding from exit holes. 

 Many larvae were collected into fifty per cent, alcohol. They were 

 from eleven to thirteen millimeters in length. 



A large bundle of sprouts and seedling stems of Prunus avium 

 and P. domestica 0.7-4 cm. in diameter was cut; and the ends of the 

 sticks were stuck into vessels of soil. The soil in one vessel was 

 made very wet and that in the other was about in condition for 

 good tilth. 



Several P. domestica and P. avium seedlings 1-4 cm. in diam- 

 eter were found which had the cambium near the ground almost 

 entirely destroyed by the numerous short-trip zigzag mines 

 crossing and recrossing each other in that region. 



On May 25 only about a sxith of the larvae were still in the host 

 and by May 30 none were found under the bark; the mines were 

 found occluded or closed. After a careful examination of the 

 surface soil under clumps of Prunus sprouts and seedlings quite a 

 number of small yellowish, somewhat fusiform and barrel-shaped 

 pupae were found. Some were collected into alcohol. They 

 were about 2.7 mm. in length and about 0.9 mm. in diameter 

 (Plate 10, fig. i). On examination of the surface soil in the 

 vessels into which the Prunus stems had been inserted large num- 

 bers of the same pupae were found, indicating that they must be the 

 pupae of the cambium mining larvae. In the vessel where the 

 soil had been kept excessively wet a number of dead larvae were 

 present, showing that excessive moisture prevents pupation in 

 some cases. The stems were carefully removed and examined 

 but no larvae could be found in them, while mines and exit holes 

 were numerous. One of the vessels containing the pupae in its 

 soil was placed in a cheese-cloth cage, and cheese-cloth was tied 

 over the tops of the other vessels. 



Pupae collected under Prunus shrubs on June 4 sank at once 

 when dropped into alcohol while those collected on May 25 usually 

 floated several minutes before sinking. The puparia seemed more 

 tightly filled by the pupae on June 4 than before. On holding the 

 vial containing pupae up to the light fully formed fly-like imagines 

 could be distinctly seen. Twenty-five of the pupae collected under 



