DISEASES DUE TO FUNGI 67 
no doubt that the loss of vigour caused by this fungus is 
the cause of considerable financial loss. Infection takes 
place at the crown or collar of the plant, frequently at 
the graft. The disease appears as a slight discoloration 
of the bark, which later becomes water-soaked and black. 
Gradually the lesions girdle the stem and cracks appear 
in the sunken infected area. The disease spreads down 
into the roots and the diseased tissue becomes brown and 
powdery. Such developments have a detrimental effect 
upon the health of the plant, which becomes weak and 
spindly and produces small, valueless flowers. 
The disease is caused by Cylindrocladium scoparium 
Morgan (34), which produces cylindrical, one-septate 
spores in characteristic heads. Over-watering is highly 
favourable to the disease, and alternating periods of 
drought and excessive dampness should be avoided. 
The disease organisms live in the soil and may be de- 
stroyed by steam sterilization. To some extent it may 
_ be controlled by planting grafted individuals, so that 
the union of scion and stock is above the soil. 
ROOT ROTS 
The roots of most plants are susceptible to disease 
when the soil conditions are wrong. The extent of root 
rot may be slight and produce results equivalent to those 
produced by root pruning. On the other hand, should 
the rot get the upper hand, death of the plant is the 
ultimate result. Numerous root-rotting fungi have been 
recorded, and the list is by no means complete. An 
excess of soil water, and consequently lack of aeration, 
is a potent factor in inducing root rot, and beds rich in 
organic matter, especially of a nitrogenous nature, favour 
the disease. Generally speaking, root rots due to fungi 
may be divided into two main classes—those caused by 
wound parasites and those caused by fungi capable of 
attacking healthy roots in the absence of wounds. Thus 
soil insects, by opening up wounds in the roots and stem 
