420 
THE GARDENERS’ 
Microscopic examination shows the following 
etai rst indication of 3 їз 
plasmolysia, followed by the complete disappearance 
of the chloroplasts from the palisade-cells of the leaf, 
ts during the first 
by the appearance of a hig 
preg теди g sphere in 
early period of formation, the centre of the sphere 
presents a granular appearance, and when broken 
up and treated with s solution of iodine, the granules 
rove t h grains 
from the a chlorophyll grains, and 
during formation of the sphere. 
spheres, the enclosed starch grains h 
commen: dissolved, * their substance 
the чача 888, this stage a section ерем 
а diseas 
reticulated, the configuration 
stantly changing after the fashion of the 
stantly 8 a roun ed, eve 
i 1 
tained. Vacuolation takes 
laced in a 1 per cent, solution of osmic acid instead 
of water, which, taken alone, is sufficient proof that 
the spheres in question not of an ameboid 
nature, In some instances, instead of on: теңин 
apheres are are formed i in a cell, each т undergoing 
lation, b small in Mets 
he composition of the iske is proved by the 
action of reagents to be complex, and although I 
have sometimes spoken of the tannin-vesicles, 
it must be clearly understood that I do not intend to 
convey the idea that "n consist entirely of tannin, 
although agreeing in y respects with the struc- 
кн — eee by Klercker.“ 
nin is — is shown by the following 
reactions: ga ichromate produces a bright- 
brown ых. ыб in water; 
solution of cupric acetate causes a 
e; 
ns the 
spheres, but as previously stated, does not prevent 
vacuolation, Finally, the accumulation of methylene- 
blue by tannin-bearing cells, as pointed ont 
deep blue after remai an exceedingly dilute 
aqueous solution of шен ийүү for twenty-four 
hours ; i green ma ted for methylene- 
blue with good results. All the above reactions are 
most before vacuo! takes place ; in fact, 
when the vesicles are fully distended, but 
coloration by any 
mentioned, the other hand, f 
presence o 
proteids in the spheres is suggested by the rapid 
staining of the mass, on the application of such 
reagents as eosin, carmine, iodine, &c. Carbo- 
hydrates are also in all probability present, 
The spheres originate in the cell-sap, and their 
presence depends entirely on plasmolysis of the cells, 
which occurs during the earliest phase of the disease. 
becomes turbid, 
een In some 
tter becomes uni- 
minute, spherical masses, and in 
о. celle filled 
; here, how- 
* Studien tiber 
r die Gerbstoffvakuolea, Tübinger Inaugur.- 
T Ueber Aufnahme von Anilinfarben in lebenden 
Unters, a, d. bot. J Instit, гц zu Tübingen, bd, ii., p. 179, Zellen, 
ever, the resemblance ends, as the minute spheres 
are found to form only a single layer lining the 
primordial utricle, and not completely filling the 
cell, as in Plasmodiophora; furthermore, reagents 
show that the spheres consist of tannin, and not 
protoplasm. In other cases, the inside Е the epi- 
plasm, and sometimes aleo the cell-w whic 
along ‘with the other parts, E бнер 
—is covered with tubes ог variously branched, very 
slender rods of a brown colour, Usually, however, 
the epiplasm or primordial utricle becomes entirely 
disorganised, drops of tannin accumulate at various 
pointainitssubst Г panied іп many instances 
by minute crystal-like bodies, These Агача = 
appear, leaving holes in the membrane, which, 
with others previously present, produce an ‘neal ar 
reticulation, the whole being of colour, 
The nucleus of the cell frequently remains un- 
ed ughout the entire cycle of disease, 
In Viala and Sanvageau's account of the Vine 
disease previously alluded to, vacuolated tannin- 
vesicles and the reticulated primordial utricle have 
been respectively interpreted as constituting the 
аем phase of their supposed Piasmodiophora 
The чере seria of the disease under considera- 
tion was аб first pursued along lines suggested b 
the Рад i idea that & 
0 
existence of the hypothetical fangus, that a search 
was made for bacteria, but with а like result, 
Final, failing v induce the disease in healtby 
fungi or mie this was коерык аз 
8 f the absence of t 
ms, 
this — Mr. W. Watson, assistant curator, 
Roya al Gan s, Kew, whom I take this ad 
of ang r^. numerous practical hints during this 
investigation, suggeste 
plants as a probable cause of the disease, @ 
on this suggestion, the бенен qe somewhat drastic 
experiment was undertaken 
A young healthy — ‘of Habenaria Susanna, 
К, Br., perfectly free from “ spot,” and which, up to 
the date of the experiment, had been growing in a 
house having a temperature ranging between 75° and 
80° 
parti 
unipjar is of the upper surface of the 
leaves, the a ant—along with the pot in which it 
gre then placed in a sink and covered with 
а bell-jar, and cold water from a tap allowed to flow 
over the bell-jar for twelve hours, during which time 
periment, the points on the surface of the leaves 
originally covered br particles of ice were pale in 
colour, and on examination under the microscope, 
plasmolysis of the cells of the palisade-tissue ue, and 
деде: chloroplasts, were found to have 
taken place. The remaining spots were examined 
at intervals, A within four days, every phase of 
2 disease d, agreeing in every respect 
with the r already described. 
The foregoing experiment showed that а sudden 
fall of 30° of te 
t with the same 
species of plant, all the — | bathe as nearly as 
possible counterparts of those 
? Fahr., were placed on the leaves 
2 of particles of ice. A diseased spot a 
point previously occupied by a drop of w. 
— отед. all “oie nae ng чын tenia a of 
true "s experiments, 
with the object et determining. ee minimum depres- 
CHRONICLE. 
[Остовкв 12, 1895, 
sion of temperature ил rng to produce the disease, 
showed tha e formation of 
igh temperature, diseased 
much smaller reduction ч [temperature than p 
previously accustomed а comparatively low 
emperature 
I 
irregularity 
in the appearance of 
in different he 
specimens "i П 
nducted under precisely F 
for three days in а dry place, it was found imponible 
to produce spot by the method mentioned abore, 
whereas with a similar specimen removed from the 
same plant, and having the peeudo-alg placed in 
ter at once, ae: dev veloped. could be 
produced i in 5 ur md 
exper erim were ma — 
supplied with water and kept in a low temperature, 
usually resist all attempts to produce “spot” 
artificially, 
It may be mentioned that, other 2 а 
the experiment is conducted n atmosphere 
h moisture, This with м 
experience of gardeners, who state that “spot” is 
most A in foggy weathe r. 
Abbey * due to an organism named 
Plasmodiophora Tomati. 
SUMMARY, 
The Orchid disease known as spot is of nof 
parasitic arig: the initial cause being the presenc? 
i water on the surface of the leave 
mperature is exceptionally lov, 
The e 
water under the above-mentioned 1 aadal is to 
cause plasmolysis of the cells of the leaf und A 
tann 
complete ае tion of the cells. 
“Spo is Brenda st sense of the term, . 
Would pe the effects of exceptional mye 
conditions on the living of оа of 
and 
э high perat , m : 
ot sufficient con 1 ; 3, water” 
ing or spraying with a falling instead of & rising 1 
temperature. "ge see, ба Й of 
ssistant | » "4 ied bf 
tiem Octo [The original is  ассошра 
coloured plate . the microscopical 
referred to.—Eb ] 
—³ ́ — — 
LELIO-CATTLEYA X сохи 
= SUPERBA (1-С. x ELEGANS 
NERIZ,C. WARSOEWIOZIÍ (GIGAS)?) 
nts J: 
Ovr illustration (fig. 74, р. 421) re pybridf | 
gt ори s gabe one of p fine the 
the season, and which was xhibited B 
pes 
* The “drooping” disease ip Tomatos, Journ: 
vol xxx., p. 360 (April 25, 1895). 
n Sondusting the experiments * e. 
= 
grown in the l 
