April 20, 1872.] 
THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. 
853 
I have myself noticed it upon a plum-tree, and—which 
is a very rare occurrence—upon a young oak.* 
On the 22nd the honoy-dew was sufficiently abundant 
in the morning to fall in large drops upon the ground. 
It was a shower of manna. At three o’clock the saccha¬ 
rine matter no longer remained fluid iipon the leaves 
wdiich were exposed to the sun. It had sufficient con¬ 
sistency not to adhere to the fingers when touched ; it 
formed, in fact, a sort of transparent and flexible 
varnish. Out of the sun the honey-dew still retained 
its viscous condition. 
On the 23rd, at seven in the evening, several leaves at 
the extremity of a branch were washed and sponged, so 
as to remove all the saccharine matter. At six o’clock 
the following morning the leaves which had been washed 
seemed free from honey-dew, but, on examination with 
a lens, minute glistening dots, due to very small drops, 
were observable. At seven the same evening the appear¬ 
ance of the leaves remained the same. The day had 
been warm ; the temperature in the shade 81°. 
On the 25th numerous spots of honey-dew were 
scattered over the leaves, but there was none xipon the 
principal veins; at three o’clock the temperature was 86°. 
During the night a violent shower removed a great 
part of the honey-dew formed during the evening. It 
became, therefore, impossible to follow, as had been pro¬ 
posed, the progress of the secretion upon the leaves 
washed upon the 22nd. A swarm of bees settled upon 
the tree. 
On the 27th, the whole of the honey-dew had dis¬ 
appeared, in consequence of the rain which fell during 
the evening of the 26th. The temperature had stood at 
between 62° and 75° F. On the morning of the 28th 
the leaves bore numerous spots of honey-dew, which had 
made their appearance during the night. On the 29th 
it had increased; on some of the leaves it occupied a 
third of the surface. At two o’clock the temperature 
was 84.°. On the 30th the honey-dew was very abundant. 
The lime-tree remained covered with it till the com¬ 
mencement of persistent rains, which took place at the 
beginning of September. 
On two occasions, namely July 22nd and August 1st, 
honey-dew was collected by washing the leaves. The 
solution after treatment with lead subacetate to precipitate 
albuminous and mucilaginous matters, yielded a syrup 
in which crystals of sugar formed. On examination it 
contained a sugar analogous to cane sugar, and also a 
reducing sugar. By fermentation with yeast the two 
sugars disappeared completely. In the fermented liquid, 
however, a substance remained possessed of very strong- 
powers of right-handed rotation. This proved to he 
dextrine, already announced by Berthelot as existing in 
the mannas of Sinai and Kurdistan, and subsequently by 
Buignet in a manna occurring in “ tears ” {marine en 
larmes). 
I have endeavoured to find mannite, and with especial 
care, because Langlois, an experienced observer, has 
found it in a saccharine matter collected from the leaves 
of a lime. Mannite is so easy to detect that I have not 
the slightest doubt as to its presence in the product 
studied by Langlois. 
Optical observations have shown that the reducing 
sugar detected in lime-tree manna is not glucose (grape 
sugar), of which the rotatory power is 56° in the right- 
handed direction, but bcvulose (inverted or fruit sugar) 
wdiich has a left-handed rotatory power of 26°. 
Taking in consideration those substances only wdiich 
rotate the polarized ray, the composition of honey-dew 
w ill be :— 
* A saccharine substance exudes from the leaves of 
Quercus manifera, iu Kurdistan. (Lindley, Dot. Reg., May 
and June, 1840.) Such a secretion from the oak is more than 
once alluded to by Latin'poets. In the Golden Age—“ Durae 
quercus sudabunt vescida mella.” (Virg. Ec. iv. 30.) Martin 
remarks (Virg. ii. 36), £; It is no uncommon thing to find a 
sweet glutenous liquor on oak leaves.” W. T. D. 
July 22. 
August 1. 
Cane sugar. 
48-86 
55-44 
Inverted sugar 
28-59 
24-75 
Dextrine . 
22-55 
19-81 
100-00 
100-00 
These analyses show that the composition of honey-dew 
collected with several days’ interval has not remained 
the same. No doubt one has no right to expect that the 
composition should remain precisely identical; wdiat, 
how r ever, is remarkable, is the analogy which exists in 
composition between the honey-dew of the lime and the 
manna of Mount Sinai analysed by Berthelot. Its 
composition is, in fact, identical with that of the honey- 
dew collected on August 1st. 
Cane sugar 
• • 
• • 
• • 
55 
Inverted sugar 
• • 
• i 
0 0 
25 
Dextrine 
• • 
• • 
0 0 
20 
ICO 
It is a discovery not without interest to have found the 
manna of Mount Sinai in the Yosges. 
In attempting to compare by analysis the quantity of 
honey-dew existing upon the leaves of the lime which 
was affected vdth the saccharine matter contained in the 
leaves in their normal state, he arrived at the following- 
result :— 
In 1 Square Metre of Healthy Haves :— 
Cane 
Inverted D ex trine. 
Sugar. 
Weight in 
Sugar. 
Grammes. 
3-57 
•86 0-00 
4-43 
In Iloney-clew Collected from ditto 
.-— 
13-92 
7-23 5-62 
26-77 
Difference :— 
10.35 
6-37 5-62 
22-34 
The amount of manna, therefore, which exudes from 
the affected leaves is considerable, especially when one 
takes into consideration the amount of dextrine, a sub- 
tance which does not exist in the healthy leaves at all.* 
From calculations made upon a tree of the same age and 
size, the leaves of the affected lime-tree v-ould have a 
surface of 240 square metres, or rather of 120 square 
metres (equal to 145 square yards), since the manna only 
covers one side of their surface. It would result from 
this, that on July 22nd, 1869, the lime bore two to three 
kilogrammes (equal to about 4 lb. to 7 lb.) of honey- 
dew, reckoned in a dry state. 
In the normal conditions of vegetation the saccharine 
matters elaborated by the leaves, under the influence of 
light and heat, are distributed through the organism of 
the plant wdth the descending sap. In the abnormal 
state, which determines the production of the honey- 
dew, the saccharine matters are accumulated at the 
upper surface of the leaves, either because the movement 
of the sap is interrupted, or because it is retarded by 
the viscosity resulting from the formation of dextrine. 
The production of honey-dew cannot be due merely to 
meteorological influences—to the effect of warm and 
dry summers. No doubt the lime of Liebfrauenberg 
secreted it during a summer when there were periods 
of high temperature, accompanied by great dryness ; 
we must not, however, lose sight of the fact that it was 
a single tree that was attacked by the malady, and that 
at a little distance there were limes which were perfectly 
healthy. 
It has been supposed that aphides, after having drawn 
the honey-dew from the parenchyma, discharge it again 
* The occurrence of dextrine in the living tissues of 
plants is at the most hypothetical. Sachs, Ihys. J eg. (Fr* 
cch), 377. 
