VASCULAR FLOWERLESS PLANTS. 83 



their function, the latter develop into the frond. These bodies 

 are, therefore, only found on these plants whilst in a young 

 and nascent state j in the mosses, on the contrary, antheridia 

 and pistillidia are found on the fully developed plant. 



115. The fronds of the diiFerent species of ferns are circi- 

 nate, or rolled up from the apex to the base in the bud, in a 

 beautiful spiral. This disposition of the plant is analogous 

 to that of the Droseraceae and Cycadaceae amongst flowering- 

 plants. Ophioglossum vulgare is, however, an exception, as the 

 fronds are straight, and never rolled up or oircinate in the bud. 



116. The young unrolled fronds are copiously covered with 

 membranaceous, chaffy scales, but, as the heat and light of the 

 sun increase, the scales fall off, and the fronds gradually un- 

 roll, until at length their entire surface is spread abroad in 

 the atmosphere. 



117. After the vegetative functions of the plant have been 

 exercised for a certain length of time, and the frond has ac- 

 quired its maximum growth, certain parenchymatous cells 

 situated along the- margin or on the under surface of the 

 frond begin to manifest their reproductive functions. These 

 cells develop into regular organized bodies called ihecse (Btxti, 

 a repository), which contain the spores or reproductive mat- 

 ter. The thecse invariably spring in clusters from the nerves 

 or veins of the frond. The spores are ordinarily very small, 

 and are free in the interior of the thecse at every epoch of 

 their development. 



118. The clusters of thecse are called, botanically, sori (sorus, 

 a heap), presenting to the naked eye the appearance of circu- 

 lar or oblong masses, or heaps of powder. This pulverulent 



