228. VINES 
the appearance of adventitious, or air roots along 
the main cane. These denote a desire on the 
part of the plant for something it needs but is 
not receiving; the ground roots may not be in a 
condition to supply the tops with food, or a 
cold, sour, or impoverished border may not 
supply sufficient nutrition. Occasionally, though 
very rarely, these roots result from overheating 
and excessive moisture. Although they indi- 
cate poor health, they should not be removed; 
they will dry up and die when the wood is ripening. 
I have already described the preventive measures 
against mildew. Do not neglect to practise 
them rigorously, for the disease is very trouble- 
some when once started. 
Splitting is a disease, sometimes the result 
of not thinning the berries, and the subsequent 
crowded condition, but more often caused by an 
overflow of sap into the bunches, resulting in a 
cracking or splitting of the berries. The best 
cure for this is to cut, with a sharp knife, about 
half way through the shoot between the affected 
bunch and the maincane. This usually reduces 
the flow of sap sufficiently; but if the berries 
continue to split, cut a little deeper. 
Being easiest to grow, the Black Hamburg is 
the most common variety of greenhouse grape. 
