THE THREAD PLANTS. 93 
Laurentian period, enclosed cytods were probably the first to 
arise (vol. i. p. 345), by the naked, structureless, albuminous 
substance of the Monera becoming condensed in the form of 
a pellicle on the surface, or by secreting a membrane. At a 
later period, out of these enclosed cytods genuine vegetable 
cells probably arose, as a kernel or nucleus separated itself 
in the interior from the surrounding cell-substance or 
plasma. 
The three classes of Green Aleve, Brown Alge, and Red 
Algze, are perhaps three distinct classes, which have arisen in- 
dependently of one another out of the common radical group 
of Primzeval Algze, and then developed themselves further 
(each according to its kind), and have variously branched 
off into orders and families. The Brown and Red Alge 
possess no close blood relationship to the other classes of the 
vegetable kingdom. These latter have most probably arisen 
out of the Primeval Algee, either directly or by the inter- 
mediate step of the Green Algz. 
It is probable that Mosses (out of which, at a later time, 
Ferns developed) proceeded from a group of Green Algez, 
and that Fungi and Lichens proceeded from a group of 
Primezeval Aloz. The Phanerogamia developed at a much 
later period out of Ferns. 
As a second class of the Vegetable Kingdom we have 
above mentioned the Thread-plants (Inophyta). We under- 
stood by this term the two closely related classes of Lichens 
and Fungi. Itis possible that these Thallus plants have 
not arisen out of the Primeval Algz, but out of one or 
more Monera, which, independently of the latter, arose by 
spontaneous generation. It appears conceivable that many 
of the lowest Fungi, as for example, many ferment-causing 
