804 
Journal of Agricultural Research 
Vol. XXVIII, No. 8 
glands. Still another class of disorders might be described as genetic, since 
they either are inherited or are closely connected with genetic factors. 
If organisms are involved in crazy-top, they doubtless are able to live con¬ 
tinuously in the cells without destroying the protoplasm, like the bacteria that 
produce crown-galls. Organisms that cause permanent disorders must be 
adapted or adjusted in some manner against increasing to large numbers that 
would destroy the host-plant. Since it would be to the advantage of such 
parasites to injure their host-plants as little as possible, the tendencies of natural 
selection with parasites as well as with the plants themselves would be in the 
direction of less serious injuries. Thus a condition of immunity might be reached 
in which little or no injury would be apparent. An immunity of tolerance 
might exist in some species of plants and an immunity of resistance in others. 
The different degrees to which the adjoining areas of leaf tissue are affected, 
as shown in the mottled discolorations of the leaves in the mosaic diseases, would 
indicate delicately balanced conditions of the tissues in relation to the disease. 
It is easy to understand that an organism or a chemical compound thus limited 
in its existence to the vegetative protoplasm of the plant might be very difficult 
to isolate. That growth disorders are not conveyed through the seeds may mean 
that the cause of the disease is too delicate or unstable to survive a resting stage. 
One of the growth disorders of cotton is limited to cool weather in the spring 
and fall. Malformations induced by chemical substances may be seen in the 
formation of galls through secretions or excretions of insects, mites, or nematodes. 
The growth disorders might be considered as slight, generalized gall-formations. 
Investigators of animal nutrition now recognize special growth-controlling 
substances called vitamins and hormones whose absence or deficiency renders 
development abnormal, and results in such diseases of children as rickets, acro¬ 
megaly, or cretinism. Some of the vitamins that are necessary for animals are 
derived from plants and may have their proper functions in the growth of the 
plants, so that plant disorders might result if the vitamins were destroyed or 
counteracted by other substances. Thus an anti-vitamin substance or a physio¬ 
logical disturbance that destroyed or disturbed the vitamin relations might be the 
cause of a growth disorder of a plant. 
On account of the nature of the plant organization, growth is not restricted to 
one period, but is continued or renewed at intervals, so that a growth disorder is 
continued or repeated through the life of the plant individual. Thus it is possible 
to understand that such disorders as crazy-top may be similar to some of the 
diseases of children or of young animals. But until the causes of the plant dis¬ 
orders are more definitely known, investigation must be directed largely to the 
symptoms, as manifested in the behavior of the plants. Hence, a comparison of 
crazy-top with other growth disorders apparently is the best way to facilitate the 
further study that is needed. 
GENERAL FEATURES OF CRAZY-TOP 
Reference was made in the Journal of Heredity for October, 1923, to the crazy- 
top disorder in Arizona as possibly analogous to other growth disorders of cotton 
that have been studied in China and in Haiti. Further observations in Arizona 
showed additional features in common with the foreign disorders. As indicated 
by the popular name, the plants infected with crazy-top undergo a sudden change 
in their habits of growth, the upper growth of affected plants becoming abnormal 
and strikingly different from the earlier normal growth of the same plants. (See 
PI. 2.) 
The name acromania is suggested as a technical equivalent of crazy-top, con¬ 
veying the same idea of abnormal behavior of the upper part of the plant. 
