56 CHAPTERS ON EVOLUTION. 



studied from one aspect, but exhibiting the closest alliance with 

 another type or plan when different details of structure are regarded, 

 prove in the clearest fashion that continuous development has beer 

 the " way of life " in the animal world. Whilst, lastly, the bare fact 

 that, as we trace the histories of all the types backward towards their 

 early life, the likeness grows in exactitude until it merges in absolute 

 identity, constitutes in itself a detail which is all- eloquent in favour 

 of the idea that only on one theory can the entire constitution of 

 the animal world be explained. That idea, it is needless to remark, 

 is embodied in the theory of evolution, which postulates descent from 

 a common root or stock with subsequent modification as the only 

 satisfactory explanation of the constitution of the animal world. 



The constitution of the plant world may be briefly alluded to, by 

 way of close to these observations, because the issues of botanical 

 science tend to support, in the plainest fashion, the deductions and 

 generalisations just detailed concerning the origin of the types of 

 animal life. The variety of plant life is not less profuse than the 

 diversity presented by the tribes of animals ; but, like their neighbour 

 organisms, the plants exhibit certain broad types, to one or other 

 of which it is possible to refer any single plant or group. If a table 

 of the plant-types be constructed, it will assume such a form as that 

 indicated : 



Jlf) I. THALLOPHYTES (e.g. Alga (or Seaweeds, &c.) and 



Fungi). 

 II. MUSCINE^E (e.g. Liverworts and Mosses). 



III. PTERIDOPHYTES (e.g. Ferns, Horsetails, Club-mosses). 



,J 



IT 



8 



IV. PHANEROGAMS^ 

 (higher plants) : 



A. GYMNOSPERMS, or those having no] 

 seed-vessels (e.g. Firs, Pines, &c.). ' 



B. ANGIOSPERMS, or those having 

 distinct seed-vessels : 



(a) Monocotyledons (e.g. Palm, 



Lily). 



(b) Dicotyledons (e.g. Oak, Prim- 



rose, &c.). 



n sr 

 2.<* 



Discarding all botanical technicalities, save those absolutely 

 necessary, the types of plant life may be readily enough appre- 

 ciated. If we examine such a plant as an oak, a primrose, a 

 buttercup, a palm, a lily, or, indeed, any ordinary member of 

 the plant series, we may discover that it possesses conspicuous 

 flowers, and that accordingly it may be distinguished from such 

 plants as the ferns, mosses, and fungi, in which no flowers are 



