^64 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 
AQUATIC PLANTS. 
By Prof. G. S. Boulgek, F.L.S., F.G.S., Professor of Botany, 
City of London College. 
[Read June 19, 1900.] 
'Gardenees group plants primarily according to their requirements as to 
heat, protection from frost, and moisture. They can, for the purposes of 
this grouping, pay little heed to those structural characters which 
determine the classifications of the systematic botanist. If he have an 
Orchid-house, the gardener cultivates in it only the more tropical and 
mostly epiphytic members of the order, not the terrestrial species of our 
own climate ; whilst on his rock-garden he will assemble members of 
many different Natural Orders, natives of many widely distant mountains. 
He is, in short, primarily a practical physiologist rather than a student 
of anatomy. 
The botanist, on the other hand, when he finds classification of some 
sort thrust upon him, if only as a practical necessity arising from the 
immense multitude of plants now known to science and the limited 
powers of his own memory, might seem at first free to choose the basis 
of his grouping. In early times mere size, the distinction between herbs, 
trees, and shrubs, medicinal properties, or other physiological character- 
istics, such as whether plants lived as parasites or grew in the water, 
suggested themselves. It was, however, recognised that, on merely a 
'priori grounds of abstract logic, it was desirable to discover the closest 
resemblances between plants, and that this was only to be done by taking 
into account the totality of their characters. One set of characters might 
furnish a convenient index, such as the "artificial" system of Linnaeus; 
but whilst resemblance in a few points indicated a distant affinity, it 
was recognised that resemblances in more points suggested a closer 
alliance, so that a consideration of the aggregate of characters might 
yield a "natural" system. Whilst botanists, as far back as the time of 
Magnol in the seventeenth century, spoke of the "affinities" of plants, 
and the instinct of genius in Pjernard de Jussieu had sketched out with 
great completeness a natural system of classification for flowering plants 
before 1760, it was Darwin who first showed that affinity meant 
relationship. 
The ideal at which the botanist aims in his classification is, then, the 
reconstruction of the pedigree of the vegetable kingdom. Characters 
possessed in common by large numbers of plants would seem to be derived 
from a remote common ancestor, and are suitable to distinguish large 
groups in our classification. Thus the modified bud which we term a 
floiuer and the yet more distinctive structure known as a seed characterise 
the highest, and one of the largest, of the primary divisions of the plant 
world ; the enclosure of the seed in an ovary and its fertilisation by 
means of pollen falling upon a viscid surface or stigma serve to mark off 
the higher division of the Spermaphyta, which we term Angiosperms, 
from the lower or Gyiiinospcrmia ; and the number of cotijledons, or 
