20 BULLETIN 1118, U. S. DEPARTMENT OF AGRICULTURE. 
losses. Under Florida conditions the normal temperatures occurring 
throughout the growing months seem to be suitable for infection 
and for the most part enough moisture is present to allow infection 
of very susceptible species. Unless the host is in the proper stage 
of development when there is an abundance of moisture, natural 
infection does not occur; hence, for practical purposes, it is reason- 
able to conclude that under average Florida conditions moisture 
rather than temperature is the important limiting factor in natural 
infection. ' 
GROWTH HABITS OF GRAPEFRUIT. 
A brief consideration of the habits of growth of grapefruit trees under 
Florida conditions, together with an account of climatic conditions 
occurring during the periods that a tree is susceptible to infection by 
the scab fungus, will no doubt aid materially in establishing a 
reasonable explanation of the behavior of the disease in nature. 
Bearing grapefruit trees in the neighborhood of Orlando, Fla., 
normally produce three distinct flushes of growth during the year. 
The first growth comes out relatively slowly but uniformly over the 
tree, usually during February, but in the southern part of Florida 
it may be as early as January and considerably later at more northern 
points. The emerging of blossom buds may be the first signs of 
growth, or vegetative growth and blossom buds may come out 
simultaneously, or vegetative flushes may partially harden and then 
develop blossoms on this new wood (PI. I, Fig. 1). 
If the weather is warm and conducive to the active growth of 
citrus trees there is a comparatively short time between the first 
signs of growth and the falling of petals from the latest blossoms, 
but if the weather is cold, rainy, and otherwise unfavorable for 
growth the vegetative parts emerge very slowly, and the blossoming 
period alone may extend over more than six weeks. Usually the 
greater part of the crop develops from this spring bloom. 
The second flush comes out very rapidly, usually during the hot 
dry weather of May several weeks in advance of the rainy season, 
and in a few days the leaves reach a width of an inch or more. This 
flush is much less evenly distributed over the tree and is rather 
irregular in beginning growth. There occurs at this time or some- 
what later a small quantity of bloom from which develops the June 
bloom fruit, which is quite inferior in quality. The so-called " June 
bloom" is relatively insignificant in quantity. It occurs practically 
only on trees with little or no fruit resulting from the spring bloom, 
or following a drought, or on trees which have some root or trunk 
disease. 
The third flush usually starts growing in September, well after the 
rainy season has passed. The quantity and character of growth is 
essentially the same as that occurring in May, but seldom accom- 
