324 
and development, acquiring radial struc- 
ture instead of dorsiventral, and branching 
on all sides instead of on the flanks. The 
transformation of sporophylls to foliage 
leaves following the removal of normal 
foliage has been a long-known example, to. 
which renewed attention has been directed 
by the fine illustration of such change ob- 
tained in the experiments of Professor 
G F. Atkinson. It was shown by 
Knight nearly a century ago that the sub- 
terranean shoots of the potato, upon re- 
moval of the aerial parts, rise above ground 
and develop ordinary foliage leaves and 
flowers instead of tubers; while, con- 
versely, the enclosing of aerial shoots in a 
dark chamber with saturated air gave oc- 
easion for the development of tubers, a 
phenomenon which is not uncommon under 
other than experimental conditions. A 
large number of similar transformations 
are now known. 
Besides the accumulation of a greater 
range of such phenomena, we must look to 
the future for a luminous theory of this re- 
ciprocal influence of organs. At present 
there is little that is satisfactory in the dis- 
cussion of the nature of correlation. In 
what conceivable way can the removal of one 
member act upon other parts so as to alter 
the course of its normal development ? 
What can be the nature of the stimulus 
which overcomes the diageotropism of the 
horizontal subterranean branches of the po- 
tato, and induces upright growth and the 
development of foliage ? 
Regarding the quantitative correlations 
we are quite as much in the dark ; perhaps 
more so, because of the relation of other 
functions. It is now clear that the greatly 
enlarged leaves and stems which develop 
after decapitation of a tree are in some way 
due to the increased food supply. But in 
what relation does the supply of food stand 
to these growths? Is the extensive removal 
of parts alone the stimulus which deter- 
SCIENCE. 
[N. S. Vou. X. No. 245. 
mines the revival of dormant buds and the 
formation of adventitious buds? Or does 
the increased amount of food act as the 
stimulus? But our present view of the 
movements of foods is that it is due to re- 
moval from solution, at the point where 
they are being used, of the substances 
which are needed. The using of food, in- 
deed, is looked upon as both actuating and 
regulating, inlarge measure, the movement 
of food to any point. How, then, conso- 
nant with these ideas, can a superfluity of 
food occur at any point, there to act asa 
stimulus ? Or how can excess of food in any 
way determine the increased use of food and 
so accelerate the growth of parts ? 
Pathology.—Closely connected with the 
study of the normal activities of plants are 
disturbances in the rate and character of 
function which are properly included under 
the term pathology. During the past dec- 
ade very rapid advance has been made in 
a study of those pathological changes which 
are due to the presence of a foreign organ- 
ism. Indeed, the phrase ‘diseases of 
plants’ calls to mind almost exclusively the 
effects of parasites, which cause wilting by 
mechanical stoppage of water supply, ex- _ 
traordinary growths in the form of tumors, 
destruction of chlorophyll to the detriment 
of photosynthesis, and a host of other evi- 
dent changes. Indeed, as compared with 
other fields, we are tempted to say that this 
has been over-cultivated. The difficulty, 
however, is not so much in over-investiga- 
tion as in over-publication regarding the 
distribution of the diseases and the appli- 
cation of palliatives and remedies. This 
is, in a measure, justified by the enormous 
economic value of the crops attacked. But 
one cannot help wishing that the staffs of 
our experiment stations particularly would 
give greater attention to investigations on 
the nature of diseased conditions than to 
repeating again and again the study-of 
remedial operations. 
