140 THE CULTIVATED EVERGREENS 



like constitute the symptoms of the disease. The fungi, with 

 but few exceptions, propagate themselves by means of tiny 

 structures, invisible to the naked eye, called spores, which are 

 produced in extremely large numbers. Under suitable condi- 

 tions, these germinate and reproduce the fungus from which 

 they arose. 



1. Coniferous seedling diseases and injuries 



Damping-off (caused by various fungi). 



In most regions damping-off is by far the most serious loss 

 factor in the nursery. All species of conifers are susceptible 

 to this disease, although the junipers are generally considered 

 somewhat more resistant than the remainder. The young 

 root may be rotted off soon after the seed germinates and 

 before the sprout appears above the surface, such losses often 

 being laid to poor seed germination. After the shoot has 

 appeared, a rotted area may develop at or just below the 

 surface of the ground, causing the seedling to fall over, wilt, 

 and die. This happens before the stem has become woody, 

 i.e., before the seedlings are about two months old. At this 

 time, also, the seedling may wilt and die while still remaining 

 erect, due to the rotting of the young root system. A fourth 

 variation in the symptoms is exhibited when the upper part 

 of the seedling only is rotted, infection having taken place 

 before the tip finally withdrew itself from the seed-coat. Of 

 these types, the first two are the most important. Infection 

 in a bed usually commences at certain points and spreads 

 rapidly in all directions from these foci. 



This disease is caused by certain fungi (Corticium vagum, 

 B. & C, var. solani, Burt, Pythium deharyanum, Hesse and 

 Fusarium spp. being the most usual in this country) which 

 are commonly present in the soil. They become active and 



