or at the juncture of two epidermal cells. If the spore had germi- 

 nated in the apothecium, and later came in contact with a young 

 needle, the existing germ tube oriented itself perpendicularly to 

 the cuticle and then penetrated the needle. No more than a single 

 germ tube per spore was observed. The continued branching, septa- 

 tion, and production of the intracellular mycelium is discussed later. 



RATE OF SPREAD 



The Douglas-fir plantations in New York, because of their small 

 size, were suitable for only limited studies on the rate of spread of 

 R. j)seudotsugae. Determination of the rate of spread made by a 

 disease in years past can only be made if infection on different age 

 needles can be dated. Two common methods for determining the 

 age of needles are by (1) counting bud scars which mark the bound- 

 aries of annual shoot growth, and (2) making free-hand sections 

 through the twig at the base of a given needle for counting annual 

 growth rings. Both methods give rise to errors if lammas shoots 

 develop. If lammas growth occurred late in a given year, a twig 

 might show a new annual ring consisting of large tracheids adjacent 

 to typical summer wood tracheids. Two growth rings would, there- 

 fore, be formed in that year. If lammas growth occurred early, the 

 new large tracheids would adjoin spring wood tracheids and only 

 one growth ring would be formed. However, two bud scars could 

 be counted for that year. 



Since the needles of lammas branches were often infected, they 

 were also cast and could not be used to fix the age of infection. The 

 infection stage of R. pseudotsugae was often used to differentiate 

 between normal spring growth and the later lammas shoots by 

 means of differences in the stage of disease development. 



After a relatively large sample of trees were studied a distinct 

 infection pattern developed. In every case the spread of the diseased 

 trees formed a somewhat fan-shaped pattern in the direction of the 

 prevailing wind. In the plantations studied the prevailing wind was 

 toward the East. In all but the Camden plantation, the extension of 

 the disease was up the slope from the primary infections. 



In each of the infected plantations, the primary infection occurred 

 on a relatively few trees, ranging from one to four. The infected 

 trees, if more than one, were usually close together. At Cortland, 

 however, two primary infection centers, approximately 200 feet 

 apart, were located. The disease had spread over the intervening 

 distance in two years. 



40 



