INTRODUCTION. 
Wiruin the last few years horticulturists generally have evinced 
an increasing desire to study the physiology and structural 
affinities of plants, as well as the art of growing them success- 
fully. This has arisen doubtless from the fact that such know- 
ledge tends to a clearer understanding of the laws governing 
the hybridisation of plants, and the great variety of forms 
they assume when subjected to artificial conditions. Not that 
botanical science is so far advanced as to be able to explain 
satisfactorily all the numerous phenomena of plant-life brought 
to light by cultivators. But much may be expected to result 
from the combination of science with practice. Experiments 
will be carried out in a more systematic manner, and the 
results more carefully recorded by those possessing sufficient 
knowledge to render their labours interesting beyond the com- 
mercial value or beauty of the varieties raised. Botanists can 
only theorise on many questions that gardeners have in their 
power to prove or disprove. 
Basis of Classification.—The characters upon which sys- 
tematic classification is founded, reside chiefly in the various 
modifications of the organs of reproduction and the floral en- 
velopes. Distinguishing the organs of a plant into two sets— 
those concerned in its reproduction, and those that perform its 
nutrition—we expect in a genus some material recognisable 
difference in the former, or, in other words, we put together in 
one and the same genus all the species known which have the 
different parts of their flowers constructed and arranged upon 
the same plan ; and when there are constant differences between 
plants which have the same plan of structure we say that these 
latter are distinct species. Apply this to such a clearly marked 
