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OBSERVATIONS FOR YOUNG BOTANISTS. 
XII. — Classification. 
E have now arrived at the last stage of our journey. 
Having seen how species arise in nature, we must 
attempt to classify plants. Various systems have 
been adopted, but as the young student will ere long 
make use of Sir J. D. Hooker’s Students’ Flora of the British Isles, 
we cannot do better than follow his arrangement. We will 
confine our attention to flbwering plants, as ferns, mosses, fungi, 
seaweeds, &c., would require a quite different kind of classifica 
tion. Hooker’s groups are as follows ; — 
Class I. — Dicotyledons or Exogens. 
Sub-class I. — Angiospermous Dicotyledons. 
Division I. — Polypetalae. 
Sub-division I. — Thalamiflorae. 
[This contains twenty-one “orders” or “ families.”] 
Sub-division II. — Calyciflorse. 
[This contains fifteen orders.] 
Division 1L— Gamopetalae. 
[This contains twenty-three orders.] 
Division HI. — Incompletse. 
[This contains thirteen orders.] 
Sub-class II. — Gymnospermous Dicotyledons. 
[This contains one order.] 
Class II. — Monocotyledons or Endogens. 
[This contains fifteen orders.] 
We must now study these groups somewhat in detail to 
understand upon what structures they are based. The sequence 
of the groups of the first sub-class is that of their presumed 
evolutionary history. Thus the word “ polypetalous,” though 
literally signifying “ many petals,” is used to convey the meaning 
of separate petals, as opposed to “ gamopetalous,” a term applied 
to a corolla which has its petals united or coherent. These 
words supply the names Polypetalse and Gamopetalae respec- 
tively. 
Sub-division I. is called Thalamiflorae, because the parts of 
the flower arise directly out of the thalamus, i.e., the end of the 
flower-stalk, otherwise called the floral receptacle. The freedom 
of parts is presumed to be a primitive condition, and, therefore, 
antecedent to cohesion between the parts of the several whorls. 
Entire freedom between the members of all the floral whorls, as 
in the Ranunculacece , is comparatively rare. The first instance of 
