SEPTEMBER 8, 1899. ] 
There is thus one phase of pathology 
which has yet been comparatively neglected. 
The presence of a definite organism, whose 
activities clash with those of the host to the 
injury or death of the latter, is in itself an 
incitement to investigation. But we need 
also knowledge of those disturbed func- 
tions whose causes are dependent on other 
stimuli than the presence of a’ parasite. 
Some of these are doubtless internal and 
may long remain obscure, even as the causes 
of the so-called ‘spontaneous’ movements 
have hitherto eluded observation. But un- 
questionably many plant diseases are due 
to untoward conditions of the environ- 
ment, working sometimes through chemical, 
sometimes through mechanical, sometimes 
through ethereal stimuli. This sort of work 
has been vigorously undertaken by the Divis- 
ion of Vegetable Physiology and Pathology 
at Washington, with full consciousness of 
the fact that, in order to attain results of 
value, there must be a fuller and more ac- 
curate knowledge of the normal processes. 
At this point we are confronted by the 
difficulty of determining what processes are 
normal and what are pathological. It is 
the old question of sanity and insanity in a 
new guise—a question which each is tempted 
to answer in the same way as the old Quaker, 
who remarked to his wife: ‘‘ Wife, they’re 
all daft but thee and me; yea, and some- 
times I think thee seems a little queer.” 
What action shall be chosen as a norm is a 
matter of judgment, the general vigor of 
the plant alone serving as an imperfect cri- 
terion ; imperfect, because we do not always 
know what constitutes vigor. Thus the 
study of pathology needs not only the ex- 
amination of parasitic diseases, but also a 
wide acquaintance with the proper activities 
of healthy plants in order to determine what 
derangements are produced in them by un- 
toward circumstances and obscurer internal 
causes. In the latter is an almost un- 
worked field which promises rich reward for 
- SCIENCE. 
325 
patient investigation, and that not only for 
the sake of pure science, but also for applied 
physiology as well. 
If parasitic diseases cause among culti- 
_ vated plants a loss of millions annually, is 
it unlikely that factors which can be con- 
trolled, if it is worth while to do it, cause in 
our crops a shortage ‘whose money value 
may be many fold greater? There are al- 
ready practical experiments tending to show 
that most of our field and garden crops 
steadily suffer for want of water, a want 
which windmills and water-driven electric 
pumps might often supply to great profit. 
We may not guess ; we must know by experi- 
ments on a large scale whether or not it 
will pay to supply water and to control 
other unfavorable conditions, before we 
dare recommend such measures to a prac- 
tical world. 
IRRITABILITY. 
I must now turn to a topic which is really 
deeply involved in all that I have already 
discussed, but one that deserves special 
mention. I mean the relation of irrita- 
bility to the well being of plants. Seven- 
teen years ago Sachs wrote: “ Irritability 
is universal in the vegetable kingdom. . . 
Vegetable life without irritability is just as 
inconceivable as animal life without irrita- 
bility. Irritability is the great distinguish- 
ing characteristic of living organisms; the 
dead organism is dead simply because it has 
lost its irritability.” 
It would be impossible to state the case 
more strongly. But it is one thing for him 
who has conceived a truth to state it 
clearly, and quite another thing to have 
this truth enter into the thinking and the 
experimenting of investigators. Long after 
the clear annunciation of the importance of 
irritability by the great physiologist—the 
father of modern plant physiology—too 
many were finding the chief rdle of irrita- 
bility in those reactions which by deform- 
