PARENCHYMA. COLLENCHYMA. 



119 



singly, e. g. rhizome of Ophioglossum, petiole of Dicksonia antarctica. Usually they 

 are numerous and closely aggregated. The elongated rods springing from the dif- 

 ferent sides of the intercellular space in all directions are irregularly intertwined 

 between one another, so as to form a delicate framework with air in its inter-spaces. 

 The single rods sometimes end free, sometimes they are connected by their branches, 

 or go from one side of the intercellular space to the opposite, and also adhere 

 to the latter. As regards their material, the above outgrowths of the wall are equiva- 

 lent or similar to ' slightly cuticularised membranes.' Cellulose colourings cannot 

 be observed in them, but rather they and the outermost layer of membrane which 

 connects them both behave under reagents like the limiting lamellae on the surfaces 

 of contact of the contiguous cells ; they turn yellow or brown with Schultze's solution, 

 or with iodine and sulphuric acid, and are destroyed by boiling with solution of 

 potash. It remains for further investigation to determine how far they may ac- 

 cordingly be styled parts of an inner cuticle lining the air-passages. 



Sect. 26. A definite special form oi thick-walled parenchyma is distinguished by 

 the name Collenchyma'^- It forms thick bands beneath or near to the epidermis, 

 especially in stems, petioles, and nerves of the leaf of herbaceous Dicotyledons (e. g. 

 species of Rheum, Rumex, Beta, and Chenopodium, Aegopodium, herbaceous shoots 

 of Sambucus, Labiatas, Solanacese, Begonias, petioles of Nymphsea, etc. ^), and in the 

 petioles of the Marattias '- In their typical development it is distinguished by the 

 form and structure of the walls of its cells, which are capable of division and contain 

 chlorophyll. The cells are in unbroken connection with one another; only in 

 exceptional cases (stem of Silphium conjunctum 

 and its allies) are the layers traversed longitudinally 

 by intercellular canals. In form the cells are 

 elongated many-sided prisms, with horizontal or 

 obliquely pointed ends : when they are isolated it 

 is usually plain that they are derived from elon- 

 gated mother-cells, with sharply pointed ends, 

 which are divided by permanently thin transverse 

 walls, or, as the case may be plainly stated, they are 

 chambered *. The walls are thin at the ends, and 

 along the whole of the middle of the lateral sur- 

 faces of cells, which face similar cells; but along the 

 angles they are provided with a stronger thicken- 

 ing, which protrudes into the cavity of the cell so 

 as to round it off, or it may even project further, 

 while towards the thin middle band of the wall it 

 is sloped off, or sharply truncated (Fig. 47). In 

 the stem of the above-named species of Silphium 

 the thickening extends also over the faces opposite the intercellular spaces. The 



1 [Cf. Giltay, Botan. Zeitg. 1881, p. 153 ; also 'Het CoUenchym,' Utrecht.— Ambronn, Pring- 

 sheim's Jahrb. XII p. 473.— Van Wisselingh, k la conaissance d. CoUenchyme, Ref. Bot. Centralblatt, 

 1882, Bd. XII. p. 120.] 



^ Compare Mohl, Vegetab. Zelle, p. 20; Botan. Zeitg. 1844, p. 308.— Unger.Anat. und Physiol. 



p. 148. — Sachs, Lehrb. p. 24. 



= Russow, Vergl. Unters. p. 106. * Compare Kraus, Cycadeenfiedern, I.e. p. 310 (6). 



Fig. 47. — Epidermis, «,andcoUencliyma. r/,of t1ie 

 petiole of a Begonia. The epidermal cells are evenly 

 thickened on the outer wall, where they abut on the 

 collenchyma ; they are thickened like it at the longi- 

 tudinal angles wherever three cells meet; f A/ chloro- 

 phyll grains ; p thin-walled parenchymatous cells 

 (550). From Sachs' Textbook. 



