PART II 



THE LIFE-HISTORIES AND REPRODUCTION 

 OF PLANTS 



CHAPTER XIV 



SIMPLE VEGETABLE ORGANISMS 



PLANTS exhibit a great variety of external forms, but nevertheless 

 can be collected into groups having many features, both of 

 structure and life-history, in common. In the preceding 

 portion of this book the highly elaborated structure of the 

 Flowering Plant has been almost exclusively considered, but 

 very many vegetable organisms are, of course, far simpler in every 

 way. For example, whole groups of lower plants lack true 

 roots and possess no vascular system. A specialised conducting 

 tissue consisting of xylem and phloem is only encountered 

 in the Flowering Plants (Angiosperms), in the Gymnosperms 

 (e.g. Fir-tree and other Conifers), and in the Ferns and their 

 allies (Horsetails, Clubmosses, etc.), whilst it is lacking in 

 Mosses, Liverworts, Fungi, and Seaweeds. 



The Vegetable Kingdom can therefore be conveniently 

 divided into vascular and non- vascular plants. 1 This difference 

 may perhaps be related to the fact that a considerable per- 

 centage of the latter flourish in wet or damp habitats, for it is 

 only amongst some of the larger and definitely terrestrial 

 Mosses that anything simulating the vascular tissues of higher 



I plants is developed. The majority of non- vascular plants 

 possess a type of body called a thallus which exhibits no definite 



(stem and leaves, in the sense in which these terms are used 

 among higher plants, and is in fact in many cases a mere flattened 



1 Since many so-called vascular plants possess no true vessels, these 

 terms are apt to be misleading, but long use justifies their retention. 



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