208 



BO T ANT. 



Class 9. Hepatic^. The Liveewoets. 



383. In the Liverworts the plant-body is for the most 

 part either a true thallus or a thalloid structure. When 

 there is a differentiation into stem and leaves, in most 

 cases the plant-body has two distinct and well-marked sur- 

 faces, an upper and an under one, the latter bearing the 

 root-hairs (rhizoids), by means of which the plant is fixed 

 to the ground. In this class breathing-pores are found 

 for the first time, in the vegetable kingdom. They are of 

 very simple structure (Fig. 131). 



-^S'^n ^"T^' ^ 5i?-lloiJ Liverwort ; B and C, showing brood-cups, natural 

 SJ.t; Px ^'I'^Pged to show breathing-pores. I/, a leafy-stemmed Liver- 

 wort ; a, unripe, and ft, ripened and split, spore-fruit. 



384. The leaves, when present, are usually in two rows 

 (sometimes three), and are either opposite or alternate. 

 The tissues of the plant-body show a little differentiation ; 

 the leaves, however, have no midrib or other veins, and 

 consist of a single layer of cells. The development of the 

 stem is always from a single apical cell, which repeatedly 

 divides. 



