THE PTERIDOPHYTES. 



189 



thus seen that the rhizome increases in length each season 

 only half or three fourths of an inch. Notice the roots. 

 Here true roots are first met in ascending the scale of 

 plant life. The rhizoids of all the lower plants have been 

 single cells or unbranched linear aggre- 

 gates of cells. The roots of Ferns are 

 solid aggregates ; they have an epider- 

 mis, and are made up of systems of 

 tissues closely resembling the tissues 

 of the stem. Notice that the roots 

 branch. Do you find hairs on the 

 roots? With a sharp knife make a 

 transverse section of the rhizome. 

 What is the color of the ground tis- 

 sue the fundamental parenchyma? 

 Notice the brownish tissue surrounding 

 the rhizome just inside the epidermis; 

 it is composed of lignified cellulose 

 and is known as sclerotic parenchyma 

 or sclerenchyma. Notice two well- 

 defined, almost black areas farther 

 within the stem ; they are made up of 

 very hard, strongly lignified cellulose, 

 and are known as sclerotic prosenchyma. Around and be- 

 tween these areas the fibro vascular bundles can be faintly 

 seen by the naked eye as more or less oval areas of tissues 

 slightly darker than the fundamental parenchyma. Draw 

 the section. 



Notice that the stipe is small near the origin on the 

 rhizome, enlarges considerably as it approaches the surface 

 of the ground, and diminishes gradually as it rises above 

 the surface. Of what advantage to the plant is the 

 enlargement? Cut a cross section of the stipe. Draw it. 

 Notice the appearance of the tissues in the section. An 

 imagined resemblance of these tissues to an eagle with 



FIG. 112. Cross section 

 of the root of Pterls 

 aquilina. In the cen- 

 ter is the fibrovascu- 

 lar bundle ; the dense, 

 dark tissue next to the 

 bundle is sclerotic pa- 

 renchyma ; outside of 

 this is fundamental 

 parenchyma, which, 

 together with the 

 imperfectly formed 

 bark, is often broken 

 away in the growth of 

 the root as is seen on 

 the left of the figure. 



