l'?2 THE NATURAL flTSTEM. 



with leaves, and composed of cellular tissue and soalariform ducta'fPem^ 

 mosses, club-mosses, horsetails, etc.) 

 Thallosen^ (BdUoc, green branch, ycjn>du). 



Flowerlesa plants producing in vegetation a thalhis, with no distinction 

 of stem and leaf, or root, and composed of cellular tissue only (Lichens, 

 fungi, etc.) 

 900. Classes of the flowerless plants. For the sake of analogy 

 and an advantageous comparison with the Phsenogaras, wo may also 

 regard thes? two provinces of the Cryptogams in the light of Classes 

 founded upon their different modes of fruitbearing. Thus the Aero- 

 gens constitute the class 



AngiospOB^ (ayyeiof, lyKopd). 



Acrogenous plants, producing their spores in sporangia (vessels) which 

 burst when the spore^ are mature. 

 GTMN0SP0E.S; (yvfivbc, BTiopd). 



Thallogenous plants reproduced by spores, which are produced in parent 

 cells, either forming a part of the vegetating thallus, or growing upon the 

 surface of some definite region of the thallus. 



901. Fourth division — cohorts. The six classes, as above constituted, are 

 still each of great extent, — too gTeat for the comprehension of the learner, or prac- 

 tical use. A further division is therefore necessary. To effect this on strictly 

 natural principles botanists have labored hitherto in vain. The truth is, the 

 members of these several classes are united by affinities so equable as to render - 

 it impossible to subdivide, except by distinctions more or leas arbitrary. So 

 adjacent territories, where rivers or other natural boundaries are wanting, must bo 

 separated by artificial lines. 



902. The angiospbrms are divided by De Candolle, in his great descriptive 

 work " Prodromus Systematis Naturalis Regui Yegetabilis" into four sub-classes 

 founded upon the conditions of the fioral envelops, viz. : 



1. Thalamiflorce, petals distinct, and (with the stamens) bypogynous. 



2. 0alycifiorce, petals (with the stamens) perigynous. 



3. CoroUiflorce, petals united, hypogynous, stamens epipetalous. 



4. MdnocfUamydeoi, petals wanting. 



903. The plan of Endlicher in his " Genera Plantarum" is more 

 simple and convenient, and has been followed by American writers 

 generally. He separates the Angiosperma3 into three " cohorts,'' thus : 



1. Dialypetala (Jta/lwa), to dissolve). Exogenous plants, having both calyx 

 and corolla, the latter composed of distinct petals' (polypetalous), sometimes 

 slightly cohering by the base of the stamens, rarely abortive. 



2. Gamopstake (ya/^o;, union). Exogenous plants, having both calyx and 

 corolla, the latter composed of petals more or less united. 



3. ApetcdcB (a, privative). E.xogenous plants with flowers having » calyx 

 only, or neither caJyx nor corolla (achlamydeous). 



904. The class petaliferjE may be conveniently separated into 

 two cohorts, as follows. 



1. SpadidflorcE. Endogenous plants with flowers having no perianth, or a 

 scaly one, and bomo on a thickeaed spadix, whiih is often enveloped in a 

 spathe. 



