PHANEROGAMS. 



1525 



logous structures for the purpose of reproduction, as is shown in 

 the flower, into the complex structure of which it will be unnecessary 

 to enter here. The differentiation of the tissues is also more com- 

 plex than in the Pteridophytes. 



Phanerogams include the highest types of plant life, and it will 

 be seen from the sequel how there has been a gradual advance in 

 their degree of organisation as we ascend in the geological scale ; 

 the most specialised groups only making their appearance at a late 

 epoch. 



Class I. Gymnospermte. — The first and most generalised class 

 of Phanerogams is characterised by the ovules and seeds not being 

 enclosed in the ovary, and by the early development of a distinct 

 endosperm forming archegonia in which the oospheres originate. 

 The first leaves produced from the embryo are arranged in whorls 

 of two or more ; and the wood grows from the outside, forming 

 annual rings of growth. 



In many respects the existing Gymnosperms are intermediate 

 between the Pteridophytes and the Phanerogams ; and it is practi- 

 cally certain, as we have already hinted, that in past times there 

 was a complete transition between the two series. The class in- 

 cludes the Cycads and Conifers and dates from the Devonian ; but 

 in the middle Mesozoic, which has hence been termed the " age of 

 Gymnosperms," it attained its highest stage of development, and 

 constituted the dominant type of the flora. The existing forms are 

 usually arranged in three orders, while a fourth is frequently made 

 for the reception of the extinct Cordaites. 



Order i. Cycadace^e. — Existing Cycads (fig. 1394), which occur 

 in the warmer regions of America and Asia, and also in South Africa 



Pig. 1394. — A male Cycad (3Iacroza»iia spiralis) ; from Australia. Greatly reduced. 



and Australia, are low palm-like trees, with a short unbranched 

 stem, occasionally divided into two, marked by leaf-scars. The 

 leaves form a crown, and, except in one genus where they are 



