146 DISEASES OF TREES 



a drop of water containing spores was placed amongst the 

 scales at the base of a shoot some three inches long, on 

 a twenty-year-old spruce. About twelve days later the shoot 

 was so much diseased as to droop in the manner shown in 

 Fig. 8 1, a. 



Spores sown in water on May 6th showed the first symptoms 

 of germination in eighteen hours (Fig. 82, d). When sown in 

 nutritive gelatine the spores and germ-tubes were rather more 

 vigorous (Fig. 82, e\ an extremely luxuriant mycelium with 

 spherical and clavate segments being developed both on a 

 microscope-slide and in a test-tube. Twelve days after 

 sowing, pycnidia with ripe stylospores developed on this 

 mycelium. 



The culture, which was continued till August I2th, produced a 

 dense mycelial growth, with pycnidia but no perithecia, so that 

 at that time I abandoned the hope of obtaining the latter. An 

 investigation of the diseased shoots showed that the stout vigor- 

 ous mycelium developed between the cells in the green leaves, 

 and immediately induced death in adjacent cells. In the shoot 

 axis it penetrated all the tissues, growing as both intra- and 

 intercellular filaments in the pith and cortex, while in the wood 

 it was specially abundant in the annular and spiral vessels. The 

 development of the parasite is confined to the short period 

 between the beginning of May and the early part of June. 

 Whether the pycnidia will form early or late in summer appears 

 to depend on the humidity of the air, or, in other words, on the 

 occurrence of dry or wet weather. As already stated, they may 

 ripen in fourteen days, provided the conditions are favourable, 

 as in the case of artificial cultures. 



Until we obtain the perithecia we must rest satisfied with a 

 provisional name for this new parasite. The character of the 

 pycnidia and spores leads us to place this fungus in the genus 

 Septoria, but as there is already a Septoria Pint I have named 

 this fungus Septoria parasitica. Finally, it may be mentioned 

 that in the spring of 1 890 I found this parasite on Picea Menziesii, 

 and this makes it probable that it also occurs on other species 

 of spruce. 



