THE DISEASES OF CONIFERS. 



139 



tlie mycelium of the Nectria is enabled to conquer the tissues 

 of the cortex, and even to kill the cambium and penetrate into 

 the young wood. 



If this happens all the parts above the attacked place are apt 

 to dry up and die, evidently from the stoppage of the water 

 currents up the stem ; this very often occurs with thin watery 

 twigs — so-called unripened wood" — such as may be found in 

 shaded situations, or in very damp summers. 



From the dead cortex come the white conidial cushions, 

 about as large as pin-heads, followed by the scarlet stromata 

 with immersed ascogenous fructifications. 



There are many other very interesting points about this 

 disease ; and as it is a type of an exceedingly important series of 

 diseases, very little understood in England, I shall venture to 

 direct your attention for a few minutes to some of the results. 



While relying for the most part on the researches of Hartig,* 

 so far as this particular species is concerned, I ought to say that 

 the following conclusions are based on some experience of my 

 own. 



These Necfrias, though very common indeed, are usually 

 found as decidedly saprophytic fungi, living in the dead wood 

 and cortex of fallen branches, or the parts of trees killed by 

 entirely different agencies — e.g., frost, breakage, insect injuries, &c. 

 — and experiments show that the germinal tubes developed from 

 the spores are unable to penetrate the sound tissues of living 

 branches. On the other hand, it is quite easy to infect a tree if 

 one punctures the sound cortex with the point of a scalpel on 

 which a few spores have been rubbed. The puncture kills a 

 number of cells, and the hyphae feed on the solution of food- 

 materials thus formed ; and it is only from a position of 

 advantage like this that the mycelium, waxing in vigour day by 

 day, is able to invade the tissues around, and gradually kill and 

 destroy those that are not active enough to resist it. As already 

 said, the mycelium may fail to do more than establish itself in 

 the more worn-out portions of the inner cortex, and may then 

 be cut out and cast off by layers of cork. There is considerable 

 reason for believing that it makes all the difference to the fungus 

 what kind of start it gets ; if the mycelium is still young and 

 feeble, the active tissues of the cortex may cut it out very soon, 

 * " Unters. aus dem forst-lbot. Inst, zu Miinchen," I., p. 88. 



