181

_Choripetalae_: _Iuliflorae_; _Centrospermae_; _Aphanocyclae_;
_Eucyclae_; _Tricoccae_; _Calyciflorae_.

CHAPTER XIX.--CLASSIFICATION OF DICOTYLEDONS
(_Continued_) 210

_Sympetalae_: _Isocarpae_, _Bicornes_, _Primulinae_, _Diospyrinae_;
_Anisocarpae_, _Tubiflorae_, _Labiatiflorae_, _Contortae_,
_Campanulinae_, _Aggregatae_.

CHAPTER XX.--FERTILIZATION OF FLOWERS 225

CHAPTER XXI.--HISTOLOGICAL METHODS 230

Nuclear Division in Wild Onion; Methods of Fixing, Staining,
and Mounting Permanent Preparations; Reference Books.

INDEX 237

BOTANY.

CHAPTER I.

INTRODUCTION.

All matter is composed of certain constituents (about seventy are at
present known), which, so far as the chemist is concerned, are
indivisible, and are known as elements.

Of the innumerable combinations of these elements, two general classes
may be recognized, organic and inorganic bodies. While it is
impossible, owing to the dependence of all organized matter upon
inorganic matter, to give an absolute definition, we at once recognize
the peculiarities of organic or living bodies as distinguished from
inorganic or non-living ones. All living bodies feed, grow, and
reproduce, these acts being the result of the action of forces
resident within the organism. Inorganic bodies, on the other hand,
remain, as a rule, unchanged so long as they are not acted upon by
external forces.

All living organisms are dependent for existence upon inorganic
matter, and sooner or later return these elements to the sources
whence they came. Thus, a plant extracts from the earth and air
certain inorganic compounds which are converted by the activity of the
plant into a part of its own substance, becoming thus incorporated
into a living organism. After the plant dies, however, it undergoes
decomposition, and the elements are returned again to the earth and
atmosphere from which they were taken.

Investigation has shown that living bodies contain comparatively few
elements, but these are combined into extraordinarily complex
compounds. The following elements appear to be essential to all living
bodies: carbon, hydrogen, oxygen, nitrogen, sulphur, potassium.
Besides these there are several others usually present, but not
apparently es