180 T, Holm — Dirca Palustris. 



The stem. — A homogeneous, tliin-walled cork replaces 

 the epidermis at a very early state, and surrounds the 

 broad parenchyma of the primary cortex ; this tissue (the 

 cortex) represents two distinct zones : a peripheral, col- 

 lenchymatic of about five strata, and an inner, which is 

 thin-walled ; chlorophyll abounds in both parts of the cor- 

 tex, while single (rhombic) as well as aggregated crys- 

 tals of calcium-oxalate occur only in the inner zone, 

 together with large groups of stereids. The stele con- 

 tains a broad zone of leptome with strands of stereome, 

 and some isolated strands of vessels, surrounded by num- 

 erous layers of radially arranged libriform; the medul- 

 lary rays are narrow, mostly of a single row of com- 

 pressed cells with deposits of starch. Strata of cambium 

 are developed on the inner flank of the hadrome (fig. 5), 

 thus in the periphery of the pith, an internal leptome 

 arises from this cambium, becoming gradually inter- 

 spersed with stereome. In other w^ords, we have in the 

 stem the type of mestome strands, known as '^bicollat- 

 eral." In the center of the stem is a narrow pith con- 

 taining single and aggregated crystals. 



This structure recurs in the fruit-bearing peduncle, but 

 in this the entire cortex is collenchymatic, and extremely 

 rich in aggregated crystals. 



Finally may be mentioned, that a longitudinal section 

 of the stem shows a very peculiar structure of the stere- 

 ome-strands, which do not follow a straight, but a very 

 distinctly undulate course ; a similar structure was 

 observed by Supprian^ in Peddiea FiscJieri Engl. 



The stem-structure of the Tliymelaeacece is quite 

 interesting, and Solereder^ has given a general review of 

 the principal anatomical characters. 



While the bicollateral structure of the mestome-strands 

 is a feature common to all the genera of the family with 

 the only exception of Drapetes, another peculiarity has 

 been observed, namely the so-called ' 4nterxylares 

 Phloem," leptome developed in the hadrome-rays. This 

 structure has been found in six genera of the family, but 

 not in Dirca, and it seems very remarkable that this lep- 

 tome contains also stereids. 



^ Beitrage zur Kenntnis der Thymelaeaceae und Penaeaceae, Engler 's Bot 

 Jahrb., vol, 18, p. 306. Leipzig, 1894. 



^ Systematische Anatomie der Dicotyledonen. Stuttgart, 1899. P. 806. 



