134 



MINUTE STRUCTURE OF THE STEM. 



110 



layers of the central cylinder. (The Mohl-Mirbel Palm-Type, 

 illustrated by Asparagus, Iris, Canna, Aspidistra (see Fig. 103), 



Acorns, Scirpus, Zea, etc., the 

 underground parts of Li Hum, 

 Tulipa, etc.). 



III. The bundles and the 

 fundamental tissue are plainly 

 differentiated ; the bundles run- 

 ning downwards, and gradually 

 converging at a point in the 

 middle of the central cylinder, 

 here blending with the leaf- 

 traces of older leaves, without 

 again curving outwards. (Ex- 

 amples are afforded by Trades- 

 cantia, the parts above ground 

 of Lilium, Tulipa, etc.). 



385. Guillard 1 describes six 

 types of structure in the stems of 

 monocotyledons which depend 

 chiefly upon the relations of a central zone (called " interme- 

 diate ") to the fibro-vascular bundles in the remaining portions of 

 the stem. The classification has no substantial advantage over 

 that of Falkenberg. 



1 These types will be better understood after some peculiarities in the ter- 

 minology are explained. By "pith," in monocotyledons, Guillard means the 

 central region of parenchyma ; by "intermediate zone," the active zone imme- 

 diately surrounding the central region ; by "cortical zone," the zone outside 

 the external circle of bundles and the products of the intermediate zone. The 

 six types are the following : - 



1st Type. No intermediate zone between the pith and cortical zone ; 



e. g., Polygonatum vulgare. 

 2d Type. An intermediate zone represented by different tissues : 



1. Consisting of rauline bundles ; e. g., Iris florentina. 



2. Consisting of meristemiform tissue (that is, tissue which produced 



from secondary meristem retains the shape but not the activity of 

 meristem) ; c. g., Chamnedorea elatior. 



3. Consisting of a fascicular sheath : c. g., Epipactis palustris. 



4. Consisting of the three foregoing; c. g., Acorns Calamus. 



3d Type. A single external zone of bundles, with a potential intermediate 

 zone ; c. g., Luzula campestris. 



4th Type. Common bundles in two groups : one at the centre of the stem, 

 the other forming the ordinary circle, separated from the first by a poten- 

 tial intermediate zone ; e. g., Tradescantia Yirginica. 



FIG. 110. Distribution of the fibro-vascular bundles in the leaf-shaped branch of 

 Ruscus hypoglossum. (Ettingshausen.) 



