THE THREAD PLANTS. 93 



Laiirentian 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, oixt of these enclosed cytods genuine vegetable 

 cells probably arose, as a kernel or nucleus sepai-ated itself 

 in the interior from the surrounding cell-substance or 

 plasma. 



The three classes of Green Algfe, Brown Algi=e, and Ked 

 Algae, are perhaps three distinct classes, which have arisen in- 

 dependently of one another out of the common radical group 

 of Primaeval Algae, and then developed themselves further 

 (each according to its kind), and have variously branched 

 off into orders and families. The Brown and Red Algae 

 possess no close blood relationship to the other classes of the 

 vegetable kingdom. These latter have most probably arisen 

 out of the Primaeval Algae, either directly or by the inter- 

 mediate step of the Green Algae. 



It is probable that Mosses (out of which, at a later time, 

 Ferns developed) proceeded from a group of Green Algm, 

 and that Fungi and Lichens proceeded from a group of 

 Primaeval Algae. 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. It is possible that these Thallus plants have 

 not arisen out of the Primaeval Algfe, 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 



