CELL-CONTENTS AND FORMS OF CELLS. 281 



are found. This was pointed out by Kraemer in some studies 

 on Rhus glabra and Rhus typhina (Amer. Jour. Phann., 1913, 

 p. 404), in which a herbarium specimen in the New York liotanical 

 Garden and labelled by Britton as Rhus glabra borealis shows 

 hairs which in form and size are intermediate between those of 

 R. glabra and R. typhina (Fig. 148). 



Plant hairs may be divided into two principal groups: i. 

 Glandular hairs, or those in which the summit consists of one 

 or more cells which secrete beneath the cuticle either mucilage, 

 oils, or oleo-resins, and the summit of the hair possesses a more 

 or less globular form. IL Non-glandular hairs, or those in 

 which the summit of the hair consists of one or more rounded or 

 pointed cells in which no secretion is formed beneath the cuticle. 



Glandular Hairs may be divided into five different groups : 



1. Unicellular glandular hairs consist of a single tubular 

 cell, the upper portion being more or less swollen and rounded 

 (Fig. 149, A, B). Hairs of this type occur in the Eupliorbiaceae, 

 in which they more or less resemble Papillae. In the Compositse 

 they contain a latex and appear to be connected with the laticifer- 

 ous vessels. They also occur in the Anacardiacese, Cornaceae, 

 Geraniaceae, Leguminosae, Malvaceae, Menispermaceae, Onagraceae, 

 Piperaceae, Ranunculaceae, Tiliaceae and Zygophyllaceae. 



2. Multicellular glandular hairs consist of a number of forms ; 

 either they are differentiated into a stalk and a head, or the stalk 

 may be wanting when the hair has a spatulate or clavate form. 

 These are often very characteristic for certain families, as the 

 glandular hairs in the Labiatae (Fig. 124), which possess a short 

 stalk and a head portion with eight cells, the cuticle being raised 

 like a bladder owing to the great accumulation of secretion. There 

 are a great many types of multicellular glandular hairs (Fig. 149). 

 They may be uniseriate, i.e., consisting of a series of cells with 

 either a unicellular head (Fig. 149, C, E, K, M), as in the Meni- 

 spermaceae, Araliaceae, Malvaceae, Caryophyllaceae, Geraniaceae, 

 etc., or they may be bicellular (Fig. 149, D, F, H, J, L, O), as in 

 the Cruciferae. The heads may consist of two to four cells (Fig. 

 149, G, F, F), as in the Burseraceae, or eight cells, as in the Labiatae 

 (Fig. 149, JV). Multicellular glandular hairs have been found in 

 the following families : Aceraceae, Anacardiaceae, Araliaceae, Be- 



