78 
ORGANOGRAPHY. 
BOOK I. 
are thin and membranous, and cohere in the form of a dis- 
tinct covering, as in the onion ; and, 2. the 7iaked bulb (Bulbus 
squamosus) (fig. 22, 23.), in which the outer scales are not 
membranous and united, but distinct and fleshy like the inner 
scales, as in Lilium. The outer covering of a bulb of the 
first kind is called the tunic. 
Besides the bulbs properly so called, there are certain 
leaf- buds, developed upon stems in the air, and separating 
spontaneously from the part that bears them, which are alto- 
gether of the nature of bulbs. Such are found in Lilium 
tigrinum, some Alliums, &c. They have been called bulbilli, 
propagines, bacilli, &c. Care must be taken not to follow 
some botanists, in confounding with them the seeds of certain 
Amaryllidaceee, which have a fleshy coat ; but which, with a 
vague external resemblance to bulbs, have in every respect 
the structure of genuine seeds. 
The tegmenta, or scales of the bud, have received the fol- 
lowing names, according to the part of the leaf of which they 
appear to be a transformation ; such terms, are, however, but 
seldom employed : — 
\. foliacea, when they are abortive leaves, as in Daphne 
Mezereum. 
2. petiolacea, when they are formed by the persistent base 
of the petiole, as in Juglans regia. 
3. stipulacea, when they arise from the union of stipules, 
which roll together and envelope the young shoot, as in Car- 
pinus, Ostrya, Magnolia, &c. 
4. fulcracea, when they are formed of petioles and stipules 
combined, as in Prunus domestica, &c. — (Rich. Nouv. Elem. 
134. ed. 3.) 
The manner in which the young leaves are arranged within 
the leaf-bud is called foliation, or vernation. The names applied 
to the various modifications of this will be explained in 
Glossology ; they are of great practical importance both for 
distinguishing species, genera, and even natural orders ; 
but have, nevertheless, received very little general atten- 
tion. The vernation of Prunus Cerasus is conduplicate ; of 
Prunus domestica, convolute ; of Ferns and Cycadaceae, cir- 
cinate, and so on. 
