434 



HISTORICAL GEOLOGY. 



VEGETABLE KINGDOM. 



A cell with its contents is the fundamental element of a plant, and the simplest and 

 lowest plants are the microscopic unicellular kinds ; tliat is, those made of a single cell, or 

 a few in a series, as the lower Alg.k and lowest Fungi. From these, the grade in species 

 rises through larger Algae, and other kinds consisting of cellular tissue, as the Fdngi, 

 Hepatic.e, and Mosses, to those which contain also vascular tissue, but subordinately to 

 the cellular — as the Fekns, Equiseta, Lycopods. The kinds thus far mentioned are 

 Cryptogams, or the Flowerless plants. 



The remaining plants, or those producing true flowers and seeds, are called Phamo- 

 gams. They consist of cellular tissue and woody fibers ; and also, of vascular tissue in 

 the larger part of the species. 



Ph^nogams. 



Phsenogams are divided into two sections, on the basis of the structure of the embryo 

 or seed, and the growth. In the Exogens, the embryo consists of two or more parts called 

 cotyledons. Further, as the name Exogen implies (it signifying growth by the out- 

 side), there is, after the first year, with rare exceptions, an annual addition of a layer of 

 woody tissue between the wood and bark. In a section of an exogenous stem more than 

 a year old, the wood has, consequently, rings of growth. 



In the Endogens, the seeds consist of a single cotyledon. Besides, there are no rings 

 of growth, and no separable bark ; growth goes forward mainly by the pushing out of 

 buds at the extremity of the stem or of its branches. The structure of the wood is said 

 to be endogenous. 



1. Exogens. 



Exogenous species are of two divisions called Gymnosperms and Angiosperms. 



480. 



Cycas ciicinalis, Xj^jj. 



1. Gymnosperms. — In this inferior 

 division of the Exogens, the seeds, are 

 naked and there is no stigma. The 

 fruit often consists of a cone made 

 of scales with the seeds beneath 

 the scales. They are called Gymno- 

 sperms (from the Greek for naked seed) 

 in allusion to the naked or uncovered 

 state of the seed. The inferiority to 

 other Phsenogams is manifested not 

 only in the simple character of the 

 flower, but also in the wood, which 

 contains no vascular tissue, and this 

 inferiority accords with the fact that 

 they preceded geologically other Phse- 

 nogams. The inferior division, that of 

 Cycads, is now few in species, but for- 

 merly included a large part of the com- 

 mon forest trees. The Cycads (with 

 the related Zamise) are peculiar in 

 combining the structure and fructifi- 

 cation of the Gymnosperm with the 

 habit of a Palm, and the method of 

 uncoiling the leaves as they are devel- 

 oped which belongs to Ferns. The 



