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provided with remarkable, brown, scaly hairs called ramenta. 

 The primary root does not persist and form a tap root, but 

 soon dies back, its place being taken by adventitious roots 

 springing from the stem or leaf-stalks. Most ferns are her- 

 baceous with a creeping rhizome of which the common bracken 

 (Pteris aquilina) is a good example and which sends up each 

 year one or more large fronds. Others, however, are known as 

 Tree Ferns and attain a height of some 50 feet and a diameter 

 of 1 foot with fronds 12 feet in length. In their general 

 appearance these Tree Ferns resemble some species of Palms 

 with their unbranched stems and terminal rosettes of large 

 pinnate leaves. The venation and vernation of the leaves, 

 however, is usually very characteristic, while the stem 

 exhibits a different structure from those of other woody plants. 

 The stems of the Pteridophytes contain no permanent cam- 

 bium and hence there is no secondary growth in thickness. 

 The closed vascular bundles are usually concentric and 

 arranged more or less in a circle. A section across the stem 

 of a Tree Fern therefore shows : - 



(1) A central portion of cellular tissue which often decays 



and leaves a hollow in old stems. 



(2) An outer mass composed of the bases of the fallen 



leaves and adventitious roots. 



(3) An intermediate zone between (1) and (2) containing 



the closed vascular bundles, each of which is 

 usually crescent-shaped with a dark-coloured 

 border. 



On the fern fronds and usually on their under-surface 

 are produced the little capsule-like spore-cases, or sporangia 

 which to the unaided eye look like little granules. Those 

 leaves which bear the sporangia are distinguished from the 

 barren fronds by the term sporophylls ( spore-bearing leaves). 

 The sporangia are usually collected in groups, each group being 

 termed a sorus, and in many cases they are protected when 

 young by an outgrowth of the leaf-tissue called the 

 indusium. The rupturing of the sporangium results in the 

 dispersal of the microscopic spores, each of which, on germina- 

 tion, is capable of producing a small, flat, usually heart-shaped 

 structure called the prothallium, which resembles a minute 

 cordate leaf and is usually considerably less than an inch in 

 diameter. This usually contains chlorophyll, and, developing 

 numerous root-hairs from its under-surface, becomes free 

 from the spore. On the under-surface of the prothallium 

 arise the microscopic reproductive organs, termed antheridia 



