INTERNAL HAIRS. 



223 



short lacunae 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 ofle 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 ia special cases : in Spathiphyllum 

 lancsefolium 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-narked ..plant it reaches 5-7°"", with an 

 average width .of 0.0 imni. 



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 Aroideae, in the pith and cortex of 

 species of Rhizpphora, is very remarkable. They are 

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

 in the Aroideafe, 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 Nymphasaceae, Lim- 

 nanthema, Aroideae, and Rhizopheras 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, 



Fig. 89. — Monstera deliciosa; longitu- 

 dinal section througli the petiole, d, d pa- 

 renchyma ; J — s a hair in form of an H. *he 

 main arms running perpendicularlythrough 

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

 small curved branch. From Sachs' Text- 

 book. 



• ScUeiden, Wiegmau's Archiv, 1839, Bd. I. p. 211. — Beitiage, p. 42. 



