332 
Nature and Cause of the Potato Disease. 
new beings as those of the seed ; for the seed of the plant contains 
the embryo organs or vessels precisely as we find them in the 
tuber. And this indeed must be the case with all seeds, or they 
would have no vitality ; consequently the tuber is as much seed 
as distinct * and independent germs can make it, and therefore 
not to be viewed as a slip or cutting whose duration of being is 
bounded by its parent's term of life. 
But although the tuber is trulj' a seed-vessel that contains the 
germs of future plants, and cannot therefore grow old, and its 
powers decline by reason of the parent's age, yet its continued 
use may, notwithstanding, be the source of disease. 
All plants, by whatever means propagated, are produced from 
germs containing the whole organism of the plant and this relates 
as much to slips, cuttings, and buds, as it does to seed. For 
although we know nothing of the abstract principle of life, and 
cannot therefore say what constitutes its vitality, yet we know by 
observation how it manifests itself, and that a plant cannot 
heallhil}' perform its functions unless its whole organism is per- 
fect. We also know that a plant, however propagated, is formed 
by an elongation of the whole of the vessels, which are moulded 
into a form peculiar to the individual in which they exist, and 
that the integrity of the vessels is closely connected with the vitality 
of the plant itself. Now, if a tuber contain diseased germs, and 
if these germs vegetate, the plants they produce will be more or 
less diseased, according as the germs from which they sprung 
were affected ; consequently a diseased tuber may generate dis- 
eased plants. Plate 6 represents a diseased germ, and shows how 
the disease may be communicated. The crimson spots a repre- 
sent the disease in the channel of the germ b; and stolon 2 a 
shows how the disease may affect it by its passage through the 
vascular system 3. Stolon 1 a is free from disease notwithstand- 
ing it is the offspring of the same germ as that of 2 A. The same 
germ may, therefore, generate sound and diseased stolons, and 
hence sound and diseased tubers. This arises from the locality 
of the disease, and the nature of the circulation in the formation 
of the stolons and stems, which latter has been described under 
sect. 2 and 3. If from the same germ sound and diseased tubers 
may spring, it will be readily conceived that different germs in 
the same tuber may produce the same effect ; and Plate 2 shows 
how this may be accomplished. That plate represents a longi- 
tudinal section of a tuber divided by two diametrical lines j B 1 is 
the stolen, a 2, a 3, and a 4, are portions of the tuber containing 
the germs a ; the yellow lines from stolon B show the course of 
the vessels, the crimson the course and extent of disease. Section 
* Bi.t seed piodiues varieties, tubers do not ; ergo, more distinct. — A. H. 
