Observations on Squamosis and Exanthema of the Citrus. 139 
develop adventitious roots. When these roots have become sufficiently 
stout to support the tree, the soil is removed from around the crown, and 
the trunk is severed immediately below their insertion. The basin formed 
by removing the soil from around the crown of the tree is not filled in, and 
the base of the trunk remains permanently exposed to the air. The irri- 
gation water is, of course, never allowed to flow into this basin, and the 
rains are never sufficiently abundant to maintain a dangerous humidity 
round the roots. This method of the Carcagente growers has, horti- 
culturally, its justification ; oranges produce better fruit and grow to best 
advantage on their own roots, or, which is the same thing, when grafted on 
orange seedlings. From the physiological point of view the increased 
resistance to gummosis obtained by growing the oranges with their crowns 
above ground is probably due to the fact that no change in the pressure of 
the bark upon the cambium, which is diminished when the trunk comes in 
contact with soil, occurs. When kept moist the bark becomes more sapid 
and, therefore, more elastic ; the cambium develops more freely, susceptible 
tissue may be laid down, and gummosis follow. 
2. It was early observed that the resistance of the Citrus to gummosis 
when grafted on appropriate stocks was markedly increased by high 
budding, and this method of still further reducing susceptibility to the 
disease has been advocated by the best writers on Citrus culture. High 
budding is successfully and extensively used at the present day. The fact 
that high budding in itself is capable of ensuring relative immunity to 
gummosis, even when the stock used is of low resistance, does not appear, 
however, to have been sufficiently emphasized. For instance the lemon, 
badly affected by the disease when budded low on the orange, will be quite 
resistant, ceteris paribus , when budded high on the same stock. 
Remedial measures. The important preventive method drainage is 
also remedial, not an absolute remedy in all cases, but unquestionably the 
only one, under conditions favourable for the development of gummosis, that 
is really efficient and can effect per se a permanent cure. The conditions 
necessary for the development of gummosis are growth and a super- 
abundance of water in the soil, or in other words very sapid tissues. 
Without the concurrence of the two essential factors growth and water, 
the development of gummosis to any marked extent cannot take place. 
The importance of drainage as a remedial measure is, therefore, capital. 
That in certain soils and situations, under particular climatic conditions or 
cultural methods, drainage does not prove an absolute safeguard is to be 
expected from the nature of the office it has to perform. 
Besides drainage a number of remedies have been proposed for 
gummosis, but they are in reality alleviations only. I may mention root- 
pruning, which has already been referred to as a preventive, and slitting 
the bark of affected trees. This latter method is very generally and 
