198 DERMAL AND OTHER NON-VASCULAR TISSUES [cii. 



again the secretion is produced externally, as in species of Gymnogr amine, 

 Notholaena, and Cheilanthes, giving golden or silver effects. Here the enlarged 

 distal cell forms rods of the secretion radiating outwards, which are soluble 

 in alcohol or ether. They have the effect of preventing the leaf-surface from 

 being wetted by water. A very interesting example of glandular hairs was 

 brought to my notice by Mr Boodle, in the case o{ Notholaena trichonianoides, 

 in which hairs with glandular heads and white powdery secretion appear on 

 the margins of the leaf Hairs of a similar nature and size also fringe the 

 prothallus, and they are thus common to both generations (Fig. i86). 



Fig. 185. I. Simple hair of YJ/a/'<9«/a, after Seward. 2. Hairs of Dipferts com- 

 jngata, with occasional longitudinal divisions near the base, after Seward. 

 3. Hair with massive base, of /Jz^^/erw Zti53za««7. 4. Stiff stellate hairs of 

 Trichomanes alatuni. 5. Mucilaginous hair of Blechnum occidentale dis- 

 charging mucilage from its distal cell. After Gardiner and Ito. 



Such simple linear hairs, sometimes branched, are found characteristic- 

 ally in many types of living Ferns. For instance in the Ophioglossaceae, 

 Osmundaceae, Hymenophyllaceae, and Dicksonieae, all relatively primitive 

 groups. Notably such hairs are present in certain primitive Ferns recognised 

 as synthetic types : e.g. Loxsoma, Plagiogyria, Lophosoria, and Metaxya. 

 Such facts, combined with their simple form, indicate that the linear hair is 

 a primitive feature. Sometimes, however, longitudinal divisions may appear 

 in the cells of the young developing hair, especially in its basal region. If 

 they radiate the result is a stiff and massive spindle-shaped bristle, as in 

 Dipteris (Fig. 185, 2, 3). This may be held as a derivative from the simple hair 



