240 PRINCIPLES OF BOTANY, ETC. 
sels, they become angular. In all ligneous plants 
they occur in ereat numbers, and lie in bundles 
immediately below ite eee vessels ; in some of 
the herhaceous plants, however, they are not found 
so numerous and sah in cistinct masses. They 
grow thicker towards the roct. Grew says, that he 
fe ind them near the root, aes downwards from 
right to left, but in the part of the plant above 
ground, upwards from left to right. | 
We may form an idea of the minuteness of these- 
vessels from Hedwig’s cbservation, that with a mi- 
eroscope which magnified 290 times he found the 
diameter of the hollow interstice of the tube, the 
10th part of an inch wide. ‘The real diameter, 
therefore, is no more ee: the 290th part of a 
line. How minute, therefore, must the ve sssels them- 
selves be ? 
§ 236., 
Lymphatic vessels, (Vasa lympbatica). These are’ 
found in the epidermis of plan Ss, and are of great 
minuteness, anastomosing in various ways through 
small intermediate branches. They surround the 
apertures of the cuticle, by which the inhalation 
and exhalation of vegetables is carried on; but 
they are so minute as not yet to have been filled 
with coloured liquids. Round each opening, which 
is ay shut by a moveable valve, they form a 
eircle, rarely a rhombus, asin the Zea Mays. In the 
Lilium caleedonicum those vessels run obliquely, and 
somewhat in an irrecular undulating manner, fig. 
279. Inthe common onion, (Allium Cepa), they 
run 
