172 
respectively by the Ferns and their allies, Club-mosses and 
their allies, and the isolated Horsetails, now reduced to — 
a single genus. In this group first occurred forms of 
terrestrial vegetation, which would now be called trees. We 
must lay stress upon the word terrestrial, for no one can 
now tell what glorious and luxuriant algal forests may have 
grown in primeval seas, without leaving a trace behind them, 
except amorphous masses of graphite. The Pteridophytes 
are also known as the Vascular Cryptogams, in opposition to 
the two preceding groups, which may be called Cellular 
Cryptogams. ‘They possess true roots and fibro-vascular 
bundles, and the capacity of taking on a woody structure. 
Dissimilar as the outward habit of a fern, a horsetail, and a 
club-moss may appear at first sight, they are all connected 
together by the character of their prothallus. This is a kind 
of nurse plant or preliminary stage, in which a cellular ex- 
pansion arises from the germinating spore, and in time pro- 
duces the antheridia and archegonia. From the fertilised 
archegoniwm springs the form which we call, in ordinary lan- 
guage, the fern or the horsetail, and this form, in its turn, 
gives rise exclusively to asexual spores. In the small group 
of Heterospores the extension and duration of the prothallus 
are so abbreviated that the two kinds of spores, the micro- 
spores and macrospores, approach in function very near to 
pollen-grains and ovules. But to the last antherozoids occur, 
and require water : a mark distinguishing the highest Hetero- 
spore from Phanerogams. 
_. Advancing now to Flowering plants, we have the advantage 
of being able to appeal to common knowledge. Hverybody 
has some notion of a flower and its parts. The sub-kingdom 
of Phanerogams is divided into two classes, of equal systematic 
importance, but very unequal in extent. Here, as im earlier 
instances, we must distinctly bear in mind that the vegetation 
of the present epoch is only a temporary phase of the develop- 
ment of plant-life. Palaeontology teaches us that classes now 
small in extent were once more important, and it is only by 
taking a broad view of past as well as of present life that we 
understand the relative value of the higher groups. In natural 
as well as in political history the present has its roots in the 
past, and is now determining the future. It is thus with the 
two classes of Phanerogams, Gymnosperms and Angiosperms. 
If we considered only the actual state of affairs, the Gymno- 
sperms would appear to be what they were considered in pre- 
geological times, a subordinate group. But, when we know 
that they date as far back as the Devonian beds, we see their 
importance in the great plan of creation. The Gymnosperms 
