BULLETIN 231] WALNUT CULTURE IN CALIFORNIA. 345 



Agar Plates (Surface Colonies). In beef peptone acid agar, plus 15 

 Fuller's scale, temperature 17 to 18 C., the colonies became visible 

 after forty-eight hours as minute whitish specks that changed with 

 growth to straw color (stramineus),* and at length to a lemon yellow. 

 After five days' growth at 18 C., the surface colonies measured 1.5 to 

 2.5 mm. in diameter. At this time they are straw color (stramineus),* 

 and appear raised to the eye, especially at the center, where they are a 

 deeper yellow color, or nucleated. This nucleated character of the 

 colony is quite constant, being observed even in quite small colonies. 

 The colonies are nucleated, circular, moist, shining, pale yellow with 

 regular margins. When examined with the low magnifying power of 

 the compound microscope the margins are coarsely granular, while the 

 center has a finer and denser granular structure. Under the low power 

 magnification the colony is seen to have several concentric zones which 

 probably represent different regions of growth. The margins are entire 

 or slightly undulatory. After twelve days' growth the colonies have 

 become 5 to 10 mm. in diameter and are still zoned when examined 

 microscopically. The center of the colony (nucleus) is a pale lemon 

 color, while the margin is of a still paler yellow. 



Deep Colonies. These colonies are at first white, but later become 

 lemon color. They vary somewhat in shape, being biconvex, angular, or 

 oval to circular in outline. 



Agar Slant. On acid meat peptone agar after twenty-four hours 

 incubation at 18 C. there appears a slight whitish growth along the 

 streak and on the adjacent surface of medium. In five days there is a 

 fairly abundant growth spreading on either side of the streak. Growth 

 shining, pale lemon-yellow (W. and N.)t with wavy margins. In ten 

 days growth covers entire surface of medium and often shows small 

 colonies at side of main growth. In the older tubes there sometimes 

 appears a whitening of the agar just beyond the line of growth. This 

 same characteristic was also observed on litmus lactose agar, as well as 

 on stab cultures of both of the agars. This characteristic, however, is 

 not a constant one, and was only observed a very few times. 



Agar Stab. On acid meat peptone agar after twenty-four hours at 

 18 C. growth takes place along the line of puncture and on the sur- 

 face of medium around the puncture. Growth on surface piled up, 

 yellowish. The growth along puncture tuberculate-echinulate (Ches- 

 ter's terminology). 



Carbohydrate Agars. The organism was grown in 5 per cent dex- 

 trose, lactose and glycerine agar. Shake cultures were made in each 



*Chromotaxia seu Nomenclator colorum P. A. Saccardo. 



fWinsor and Newton's specimen tints of oil and water colors. Plate 5. 



