INTERNAL HAIRS. 



221 



walls, which adjoin the outer cortex, elongate to form these hairs : they protrude as 

 blunt sacs, with i^ narrow turns, into the small passages, filling up the breadth of 

 the passage : they all curve in the same direction. The vertical distance between 

 two hairs is never less than the greatest diameter of the narrower passages. 



In the air-passages of the leaf- and flower-stalks of the Nymphceacece, in species 

 of Nymphaea (but not Nuphar), and, according to S. Hoffmann, also in the roots and 

 Rhizome, there have been known, since the time of Guettard \ branched ' stellate 

 hairs ' with pointed arms, and a firm wall, which shows numerous blunt, wart-shaped, 

 external thickenings, containing calcium oxalate ^. In the petioles and peduncles 

 the hairs arise from the simple perpendicular rows of cells, forming the corners of the 

 air-passages, which appear polygonal in transverse section : they are at different 

 heights one above another, often being separated from one another in one corner by 

 only few cells ; in neighbouring ones they are at different heights, so that on each 

 large transverse or longitudinal section several may be seen at once (Fig. 88). A 

 cell of the corner series, flattened 

 above and below, puts out an arm 

 into each of the air-passages 

 (usually 3, more rarely 4) which 

 adjoin it : these, directly they 

 enter the passage, divide into the 

 diverging pointed branches of the 

 permanently unicellular hair. In 

 the simple regular case, as is 

 most common in the petiole of x^/ 

 Nuphar pumilum, each arm 

 branches once into two almost 

 equal branches, of which one 

 turns upwards, the other down- 

 wards. In N. luteum this vertical 

 branching is often immediately 

 succeeded by a second at right 

 angles to it, so that in the most 

 regular case each arm runs out into four pointed branches, two diverging obliquely 

 upwards and two obliquely downwards. But in this, as in other species, it often happens 

 that, by the absence of one of them, or unequal development of the branches of this 

 second bifurcation, a more irregular general form is attained : also a more complex 

 branching may occur. In the larger air-passages the branches are shorter than the 

 diameter of the passages; they diverge almost at right angles, and as a rule they do not 

 touch the wall of the passages. In the narrow passages, like those of the periphery 

 of the petiole of the above species, and, according to Meyen, in all cases in Nymphaea 

 odorata and cserulea, the hairs are not at all or only slightly smaller than in the wide 

 ones ; they therefore frequently touch the lateral walls. The angle of divergence of 



Fig. 88. — Xuphar advena; transverse section through the petiole; n 

 vascular bundle, ; air-passages, s stellate hairs. From Sachs" Textbook. 



' Compare Meyen, Physiologie, I. p. 311; Phytotomie, p. 200, Taf. IV.— Tiecul, Ann. Sci. 

 Nat. 4 ser. torn. IV. 



- According to a note by H. von Mohl. communicated to me. 



