SCLERENCHYMA AND SCLEROTIC CELLS. 42$ 



chlorophyll. Still stouter, shortly-branched fibrous cells stand in the palisade-parenchyma 

 on either side of the leaves of Statice purpurea, approximately at right angles to the 

 surface, but without reaching the epidermis. 



Sect. 127. Short sclerenchymatous elements occasionally appear in the primary 

 structiire of the Phanerogams, united, like the fibres, to form hypodermal strands 

 or sheaths, or as portions of them. This is the case with the hypodermal layers 

 in Palm-stems (Cocos, Elais, Astrocaryum vulgare, Mauritia armata, Klopstockia, 

 Chamsedorea Karwinskiana) mentioned at p. 127, which are interrupted under every 

 stoma by thin-walled parenchyma, and also with the annular layers also mentioned 

 at p. 127, in the stems and roots of Aroidese, and with the stegmata. Some special 

 phenomena to be placed in this category are described by Pfitzer ' in the case of the 

 foliage-stem of Restiacese. Restio diffusus has single-layered double longitudinal 

 rows of rod-shaped, radially elongated sclerenchymatous elements, which alternate 

 with longitudinal bands of chlorophyll-parenchyma. 



Willdenowia spec, and Leucoplocus show the same structure, with the difference 

 that the hypodermal layers are broader, consisting of 3-4 rows. In Elegia nuda and 

 species of Restio (R. tecLorum, paniculatus, incurvatus, &c.), Thamnochortus, Will- 

 denowia, Hypolsena, Ceratocaryum, and Leucoplocus, the very large air-cavities under 

 the superficially situated stomata are bordered by a ring of sclerenchymatous elements, 

 elongated and placed at right angles to the epidermis, and converging in a curve 

 towards the inside ; they are in uninterrupted lateral connection with one another, 

 with the exception of slit-like interstices, by means, of which communication between 

 the stomatal cavity and the intercellular spaces of the neighbouring parenchyma is 

 effected. 



In the external cortex of Dicotyledonous woody plants, short sclerenchymatous 

 elements often appear in conjunction with fibres, as annular sheaths, the formation 

 of which, on account of their connection with the processes of secondary growth, will 

 be dealt with in Chap. XV. Their occurrence in sappy masses of parenchyma and in 

 the pith of Dicotyledonous plants has been already spoken of on p. 127. The small 

 groups or nests which lie scattered in the nodes of many Potamogetons (P. crispus, 

 densus, gramineus, perfoliatus, &c.), near the vascular bundles where they anasto- 

 mose and pass out into the leaves, furnish an isolated case of the occurrence of 

 these elements. 



SjECT. 128. Among sclerenchymatous masses, which strictly speaking belong to 

 the category of hypodermal tissues under consideration, those remain to be specially 

 mentioned to which massive hard emergencies owe their strength : e. g. tough 

 prominent warts, as those of Aloe verrucosa, thorny teeth of leaves, as in Ilex 

 Aquifolium, Agave, and Aloe, and spines and thorns of the different morphological 

 categories. The epidermis itself no doubt always takes part in the sclerosis. The 

 sclerenchymatous elements are in several cases short, e. g. warts of Aloe verrucosa, 

 thorns of roses; usually they are elongated. The sclerenchyma, together with the 

 sclerotic epidermis, either forms the entire mass, or it surrounds other internal tissues. 

 E. g. the sclerenchymatous cylinder of the stem of Berberis vulgaris ^ (p. 419) sends a 



' Pringsheim's Jahrb. VII. p. 561. ' Meltenius, HymenophyllaceEC, /. c. p. 439. 



