INTERNAL HAIRS. 



223 



short lacunse of the lamina, which communicate in all directions, the branching of the 

 hairs is more complex and irregular ; they here put out radiating arms diverging on 

 different sides, which themselves again branch, and may 

 traverse many lacunae. Each lacuna, especially in stems 

 and petioles, is thus permeated by numerous hairs; they 

 may be found in every transverse section, either singly 

 or many — up to 10 or 20 — in one cavity, in the latter 

 case side by side, but always without touching one 

 another. The size and stiffness of the hairs varies to 

 a certain extent in special cases : in Spathiphyllum 

 lancffifolium van Tieghem found them the longer, nar- 

 rower, and more thin-walled, the more numerous they 

 were side by side. Their length is very considerable : 

 in the last-named plant it reaches 5-7™", with an 

 average widdi of 0.0 1""". 



The membrane of these hairs is always colourless, 

 quite smooth, more or less thickened, and stratified; 

 the inner layers, when the wall is of great thickness, 

 have shallow pits : their cavity is usually uninterrupted, 

 rarely it is partitioned by a few thin septa : the con- 

 tents are transparent and watery, with isolated granules, 

 and sometimes small crystals of calcium oxalate. 

 They closely resemble sclerenchymatous fibres, and 

 were therefore at first described as ' bast-cells ' ^ 



The occurrence of intercellular hairs, quite similar 

 to those of the Aroidese, in the pith and cortex of 

 species of Rhizophora, is very remarkable. They are 

 here usually of the H form, on the whole harder than 

 in the Aroidese, and their arms are usually solitary, 

 though sometimes 2-4 occur in one intercellular pas- 

 sage, filling it loosely. 



It is instructive that the above-described many- 

 armed hard-walled hairs of the Nymphaeacese, Lim- 

 nanthema, Aroideae, and Rhizophoras are funda- 

 mentally related to sclerenchymatous fibres, in every respect, and are only special 

 cases of the latter, distinguished by their form and distribution, and that thus their 

 earlier designation as * bast-fibres ' was not without justification, provided scleren- 

 chymatous-fibres were really meant by this name. Comp. Sect. 30. 



longitu- 

 d,d pa- 



FlG. 89. — Monstera deliciosa; 

 dinal section throutjh the petiole, 

 renchyina ; s — s a hair in form of an Ht the 

 main arms running perpendicularly through 

 the air-spaces; at the top to the right is a 

 small curved branch. From Sachs' Text- 

 book. 



* Schleiden, Wiegnian's Archiv, 1839, Bd. I. p. 211. — Beitiiige, p. 42. 



