xvi 
INTRODUCTION. 
stitutes a chief part of their value in contributing to our appe- 
tite and luxury. But botanists are ineUned to consider sugar 
not so much an original secretion, as the result of chemical 
change in the acid and mucilaginous secretions already formed, 
and we are inclined to subscribe to this opinion from the pro- 
cess we daily witness in the growth of fruits towards their 
maturerof rifftS state. 
Besides these more obvious and general secretions, many 
plants are known to secrete colouring matter, while the bam- 
boos, some species of palm, many of the grasses, and most of 
the tribe of plants producing edible grain, secrete flinty matter 
which forms a shining coat on the outside of the stalks of the 
plants, and contribute to strengthen and support their reed-like 
and slender growth. These are subjects which we cannot too 
strongly recommend to the attention of the Botanical student, 
but it would be impossible for us, in the present work, to enter 
deeply on so curious and interesting a topic : we must content 
ourselves in having given in this introductory chapter what 
we think will be considered a sufficient outline of the Science of 
Botany, to enable the student to make considerable progress, 
and to prepare himself for works in which it is treated of 
at more length. 
