INTRODUCTION TO BOTANY. 
27 
guminous plants), pith (Cycads and Pjilms*), 
balbs (Liljworts-i"). tuber.-:, rliizomes and roots 
of several different orders.^ In less abundance 
it is found throughout the winter in the bark 
and sap of trees; hence the possibility of mak- 
ing bread from the bark of trees in polar 
countries." — P. 121. 
" Under the influence of vital force, starch 
changes into gum and sugar. Sugar makes 
its appearance as a transparent fluid, which 
seems as clear as water, and is not rendered 
turbid by alcohol, but is coloured brown by 
tincture of iodine, according to the greater or 
less degree of dilution of that agent. 
" Gum appears as a yellowish, more consist- 
ent, less transparent fluid, which with tincture 
of iodine coagulates into a pale yellow colour. 
When vegetation has advanced to that point 
that gum is the latest immediate product, there 
appear in it a great many minute molecules, 
which are generally so small as to resemble 
dark points; at that time the fluid becomes of 
a darker yellow upon the application of iodine; 
but the molecules, if they are largo enough to 
show their colour, become dark-brown yellow. 
It is this mass, so transparent that it can 
hardly be seen until it is coloured, in which in 
all cases organization commences, and from 
which the youngest structure is constituted. 
It may be called vegetablejelly, and is proba- 
bly nearly the same as Pecten, the base of Gum 
Tragacanth and many other kinds of vegetable 
mucus. It is this jelly which by a further 
chemical alteration becomes the membrane of 
cells, and is afterwards the material by which 
they are thickened. 
" 'Vegetable mucilage of the chemist in part 
(Bassorine ; Salep) is a horny or cartilaginous 
substance when dry ; when moist, it swells up 
in a gelatinous manner, and becomes gradually 
diffused throughout cold water. It is trans- 
parent and soluble in hot and cold (?) water; 
in caustic alkali is perhaps converted into an 
acid. It is not affected by alcohol, ether, 
fatty or essential oils, and is not coloured by 
iodine. On one side it passes by various mo- 
difications into cellulose (ex. gr. the cell walls 
of fucoids), and amyloid (ex. gr. some kinds 
of horny albumen); on the other into amylum 
(ex. gr. the mucilage of the orchis tubers), 
and often further into gum and dextrine. 
Probably Pectine and its compounds are 
closely related here. {Henfrey.y " — P. 130. 
The matters thus far treated are elementary. 
Their combination into the external organs 
of plants is the next step. In this way is pro- 
* Sago from Cycas revoluta; Sagus Rumphii, 
farinifera, &c. 
f Lilium camtchaticum, used as food in Greenland. 
t Potato from Solanum tuberosum ; Cassava from 
JatropIiaManihot; Tari-o from Arum esculentum, &c. 
duced the cuticle or skin ; the stomates or 
pores ; hairs, scarf, glands, and prickles ; and 
also roots, stems, leaves, flowers, and fruit. 
From the minute description of the stem, we 
shall select the account given of leaf-buds, 
which besides having considerable interest, is 
also suitable to our limits : — 
"Leaf-buds {gemmae, Linn.), being the ru- 
diments of young branches, are of great im- 
portance in considering the general structure 
of a plant. Tiiey consist of scales imbricated 
over each other, the outermost being the 
hardest and thickest, and surrounding a minute 
cellular axis or growing point, which is in 
direct communication with the woody and 
cellular tissue of the stem. In other words, 
they may be said to be growing points, covered 
with rudimentary leaves, for the purpose of 
protection, and to consist of a highly ex- 
citable mass of cellular substance, originating 
in or connected with the pith or cellular por- 
tion of the branch, and having a special power 
of extension in length. Under ordinary cir- 
cumstances the growing point clothes itself 
with leaves as it advances, and then it becomes 
a branch ; but sometimes it simply hardens 
as it grows, producing no leaves, but forming 
a sharp coni(;al projection, called a spine, 
as in the Gleditschia, the sloe, &c. When 
formed it does not, however, consist of cellular 
tissue alone ; on the contrary, it has the 
same general internal structure as the perfect 
branches themselves. 
" The spine must not be confounded with 
the prickle or aculeus already described, from 
which it differs in having a considerable quan- 
tity of woody tissue in its structure, and in 
being as much in communication with the 
central parts of a stem as branches them- 
selves ; while prickles are merely superficial 
concretions of hardened cellular tissue. Spines 
occasionally, as in the Whitethorn, bear leaves ; 
in domesticated plants they often entirely dis- 
appear, as in the Apple and Pear, the wild 
vai'ieties of which are spiny, and the cultivated 
ones spineless. They occasionally branch, as 
in the Gleditschia, thus showing that the 
power of subdivision is a vital quality inherent 
in the growing point itself. 
" The spadix of the arum, the receptacle of 
nelumbium, all the forms of placenta, and 
even some styles and stigmata, are modifica- 
tions of the growing point of the bud, and con- 
sequently are analogous to unhardened spines. 
" Linngeus called the bud Myhernaculwm, 
because it serves for the winter protection of 
the young and tender parts ; and distinguished 
it into the gemma, or leaf-bud of the stem, 
and the hulb, or leaf-bud of the root. 
" The leaf-bud has been compared by Du 
Petit Thouars, and some other botanists, to 
