FREE BOOKS

Author's List




PREV.   NEXT  
|<   138   139   140   141   142   143   144   145   146   147   148   149   150   151   152   153   154   155   156   157   158   159   160   161   162  
163   164   165   166   167   168   169   170   171   172   173   174   175   176   177   178   179   180   181   182   183   184   185   186   187   >>   >|  
her part in the process, and being known as the "suspensor." Later the embryo becomes indented above and forms two lobes (_Q_), which are the beginnings of the cotyledons. The first root and the stem arise from the cells next the suspensor. CHAPTER XVIII. CLASSIFICATION OF DICOTYLEDONS. DIVISION I.--_Choripetalae_. Nearly all of the dicotyledons may be placed in one of two great divisions distinguished by the character of the petals. In the first group, called _Choripetalae_, the petals are separate, or in some degenerate forms entirely absent. As familiar examples of this group, we may select the buttercup, rose, pink, and many others. The second group (_Sympetalae_ or _Gamopetalae_) comprises those dicotyledons whose flowers have the petals more or less completely united into a tube. The honeysuckles, mints, huckleberry, lilac, etc., are familiar representatives of the _Sympetalae_, which includes the highest of all plants. [Illustration: FIG. 96.--Iuliflorae. _A_, male; _B_, female inflorescence of a willow, _Salix_ (_Amentaceae_), x 1/2. _C_, a single male flower, x 2. _D_, a female flower, x 2. _E_, cross-section of the ovary, x 8. _F_, an opening fruit. _G_, single seed with its hairy appendage, x 2.] The _Choripetalae_ may be divided into six groups, including twenty-two orders. The first group is called _Iuliflorae_, and contains numerous, familiar plants, mostly trees. In these plants, the flowers are small and inconspicuous, and usually crowded into dense catkins, as in willows (Fig. 96) and poplars, or in spikes or heads, as in the lizard-tail (Fig. 97, _G_), or hop (Fig. 97, _I_). The individual flowers are very small and simple in structure, being often reduced to the gynoecium or andraecium, carpels and stamens being almost always in separate flowers. The outer leaves of the flower (sepals and petals) are either entirely wanting or much reduced, and never differentiated into calyx and corolla. [Illustration: FIG. 97.--Types of _Iuliflorae_. _A_, branch of hazel, _Corylus_ (_Cupuliferae_), x 1. [Male], male; [Female], female inflorescence. _B_, a single male flower, x 3. _C_, section of the ovary of a female flower, x 25. _D_, acorn of red oak, _Quercus_ (_Cupuliferae_), x 1/2. _E_, seed of white birch, _Betula_ (_Betulaceae_), x 3. _F_, fruit of horn-bean, _Carpinus_ (_Cupuliferae_), x 1. G, lizard-tail, _Saururus_ (_Saurureae_), x 1/4. _H_, a single flower, x 2. _I_, femal
PREV.   NEXT  
|<   138   139   140   141   142   143   144   145   146   147   148   149   150   151   152   153   154   155   156   157   158   159   160   161   162  
163   164   165   166   167   168   169   170   171   172   173   174   175   176   177   178   179   180   181   182   183   184   185   186   187   >>   >|  



Top keywords:
flower
 

female

 

petals

 
flowers
 

single

 

plants

 

familiar

 

Choripetalae

 

Iuliflorae

 

Cupuliferae


Sympetalae

 
section
 

reduced

 
called
 
separate
 

lizard

 

Illustration

 

inflorescence

 

suspensor

 

dicotyledons


individual

 

simple

 

gynoecium

 

process

 

structure

 
spikes
 

andraecium

 

embryo

 

numerous

 

twenty


orders

 

catkins

 
willows
 

carpels

 

crowded

 

inconspicuous

 

poplars

 

Quercus

 

Betula

 

Betulaceae


Saurureae
 
Saururus
 

Carpinus

 

Female

 

wanting

 
sepals
 

leaves

 
including
 
differentiated
 

Corylus