198 Miss Dale, On certain outgrowths {Intumescences) 



The Hairs. 



(1) The stiff hairs. These are all unicellular, though as 

 before mentioned there are also stellate hairs which are usually 

 three-rayed, on the under side of the leaves. The usual type 

 consists, in longitudinal section, of a square, thick- walled basal 

 part, which is not pitted and which is inserted between the 

 epidermal cells and narrowed into a long sharp-pointed needle. 

 Above the basal part is a large nucleus (figs. 4 and 14). 



(2) The stellate hairs have essentially the same structure as 

 the simple straight hairs. 



(3) The glandular hairs are very complicated (fig. 17). They 

 consist of a very large basal cell with a central nucleus surrounded 

 by protoplasm radiating outwards towards the walls. Above this 

 is usually one cell completely filled with dense granular protoplasm. 

 This is succeeded by twenty or more cells, which in optical 

 longitudinal section appear either to be undivided or to be 

 divided by one or more walls parallel to the long axis of the hair. 

 The head of the hair consists of a group of cells of which a 

 longitudinal section usually passes through four. The two upper- 

 most of these are surrounded at some distance by a thin wall. 

 Transverse sections at different levels show, near the apex but 

 below the head, a single cell almost filled with protoplasm and 

 containing a large central nucleus (fig. 18). A section nearer the 

 base shews the circular area divided into four cells, each of which 

 has the form of a quarter of a circle. In each cell the nucleus is 

 near the innermost wall, and there is a small vacuole (fig. 19). 

 Sections nearer the base show the section to be irregularly divided 

 into six or more cells, and in some cases the area is divided into 

 as many as eleven cells, as represented in fig. 20. In these cells 

 the vacuoles are larger. Round each of these transverse sections 

 there is a thickened cuticle. Both kinds of hairs occur on the 

 outgrowths of the stem and leaves. 



Part II. Experimental. 



In order to determine, if possible, the nature of the outgrowths 

 and the conditions influencing their formation, a series of ex- 

 periments was undertaken in the spring and summer of 1899. 



Of the three old plants from which material was obtained for 

 the anatomical investigations, one had been raised from the seed 

 sent from Somaliland, the other two were grown from seed of this 

 first plant. 



For the purposes of the following experiments seeds from these 

 three plants were sown, on November 21st, 1898, in the Tropical 



