194 THE CHEMISTRY OF ESSENTIAL OILS
Lavender oil is frequently judged, as to quality, entirely on its ester-
content. There is, however, abundant evidence to show that this is a
mistake, and lavender oils can only be so classified, provided that oils
from the same district are under consideration. The fact that the true
lavender and the spike lavender grow more or less together in the same
district, causes a good deal of hybridisation to take place.
In dealing with the influence which the cross-fertilisation of
lavender and spike on the essential oil of these plants, A. Birckenstock
has also dealt with the ester question. He has pointed out that there
are also good lavender oils which contain only 20 to 30 per cent, ester.
Such oils are found in the Alps near the Franco-Italian frontier, and
the annual production (about 5000 kilos) is in Birckenstock's opinion of
sufficient importance to take the particular properties of these oils into
account. They have according to him a very fine bouquet, but little
"body". The content of linalol amounts to about 50 per cent., and is
therefore normal, but, as already mentioned, the ester content is only
20 to 30 per cent.; they are also characterised by a low specific gravity
(0*878 to 0-882), and by a considerable laevo-rotation (- 8° to - 9°);
they are, moreover, very readily soluble in alcohol (in 10 to 12 volumes
60 per cent, alcohol).
According to Birckenstock, if lavender comes below 2300 to 2600
ft. it crosses with spike, "elle s'aspique"; the hybrids thus formed
are known among distillers by the names of " lavandin " or " spigoure,"
and they represent every possible transition between lavender and
spike, according to the conditions due to altitude and state of the soil.
In this connection Birckenstock's statements on the morphological
differences between lavender and spike are interesting; lavender has a
non-ramified stalk, which is rarely longer than 16 ins.; the blossoms
are blue-violet, and have thin, heart-shaped, pointed sepals which are
shorter than the bluish calyx.
The spike plant is larger than the lavender. The stalks frequently
have several ramifications, and grow to a height of up to 32 and 36 ins.
The sepals are linear and of the same length as the calyx, which in this
case is not bluish, but whitish.
The influence of cross-fertilisation also shows itself in the proper-
ties of the essential oils, which behave entirely like mixtures of lavender
oil and spike oil. Birckensfcock has in the course of his observations
examined a whole series of oils, from typical lavender oil to typical
spike oil. He then found at the same time that as the oil approaches
true lavender oil not only the ester content and alcohol content increase,
but that also a gradual change takes place in the proportion of borneol
to linalol and geraniol; whereas in spike oil borneol predominates, it
diminishes towards lavender oil more and more as compared with
linalol and geraniol. The following are the properties of two charac-
teristic lavandin oils:—
- ^150 0'9027 ; OLD - 0
°
43'; ester-content, 6'23 per cent.; alcohol-
content (C1(;H 18 O), 34-8 per cent.; soluble in 3 volumes 65 per cent,
alcohol. - di5o 0-8995; aD - 1° 35'; ester-content, 9'12 per cent.; alcohol-
content, 36'5 per cent.; soluble in 3 volumes 65 per cent, alcohol.
According to Zacharewicz l lavender thrives best on a light, flinty-
(^1) Bull, mensuel du Synd. Agric. Vaucluse, 23 (1907), 280, and Schimmel's Report.