150 



ACADEMIC BOTANY. 



Fig. 218.— Coniforons 

 wuod ; [fitted cells. 



on account of its protoplasmic fluids. Thallogens consist 

 almost entirely of cellular tissue; it 

 abounds in Acrogens and in the lower 

 Gymnogens (Cycas, etc.). It is promi- 

 nent in the higher Gymnogens (Pines, 

 etc.) and in the Endogens. In Exogens 

 it is confined to the pith, bark, leaves, 

 and tender growing parts. 



367. Fibrous Tissue {Prosenchyma) 

 forms the woody parts of plants. It is 

 at first cellular; but the cells soon 

 thicken by internal layers, and lengthen 

 into firm, slender tubes with tapering 

 ends, which usually overlap, making the 

 wood tough and strong (Figs. 218, 219). 

 When the cells are thick and compact 

 the wood is hard, as in the Oak, 

 Hickory, etc. When they are thin and loosely 

 arranged the wood is light, as in the Linden or- 

 liime. When they cross one another variously 

 the wood is difficult to split, as in the Sweet-Gum 

 (Liquidambar). 



368, Vascular Tissue (L. vasculum, a little 

 vessel) consists of large wood-cells, either single 

 or placed end to end, forming Vessek, which are 

 also called Duds. They make the wood po- 

 rous. They are variously combined, and their 

 markings by the internal deposit (which often 

 takes the form of a thread, and is always with- 

 out tube or channel) are the same as those of 

 the cell. 



In the Melon we see various marks made by this 

 thread : (1) Annular (Pig. 220, B) ; (2) Dotted {Porous, 

 Punctate), making what are called Sieve-ducts (Fig. 220, 

 D) ; here the duct consists of several superimposed cells, 

 making it moniliform ; (3) Spiral (Fig. 220, A), in which 

 two threads wind along the inner surface of the thin cell- —FYbrou. 

 wall. The Banana (in whose Order they abound) has tissue of 

 twenty threads, forming a ribbon, which unroll alto- TraTeller's - 

 gether. Spiral ducts are called TVachece (L. trachea, tSwSb^^" 

 windpipe). 



The Fern (Fig. 220, C) has its threads parallel on the sides of the 



Fio. 219. 



