134 MINUTE STRUCTURE OF THE STEM. 



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

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

 Acorus, Scirpus, Zea, etc., the 

 underground parts of Lilium, 

 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- 

 canti.-i. the parts above ground 

 of Lilium, Tulipa, etc.). 



385. Guillard 1 describes six 

 types of structure in the stems of 

 monocot3 T ledons 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 cauline 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) ; e. g., Chamaedorea elation 



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



4. Consisting of the three foregoing ; e. g., Acorus Calamus. 



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

 zone ; e. 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 Virginica. 



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

 Ruscus hypoglossum. (Ettingshausen.) 



