122 CELLULAR TISSUE. 



Primulacese, as rrimula sinensis^, Lobelia syphilitica, Rhizomes of Scitamineae, 

 Cyperaceas (e.g. Carex hirta), Acorus gramineus. 



The same occurs in certain Equiseta. But on the other hand not the whole 

 body of vascular bundles, but each single vascular bundle is in many cases sheathed 

 round by an endodermis. This is the case both in the stem and leaf of almost 

 all ferns and many species of Equisetum, and also in the petioles and leaves (Adoxa 

 moschatellina, Menyanthes trifoliata, species of Primula), and in many stems of 

 Phanerogamic plants, as Nuphar, Brasenia peltata, Hydrocleis Humboldtii, Primula 

 auricula, INIenyanthes. Rarely an endodermis occurs in other places than those 

 named : thus in the parenchyma of the stem of many Equiseta, and in many aerial 

 roots, especially of epiphytic orchids, the parenchymatous cortex is marked off both 

 from the vascular bundle ami from the tracheal sheath by an endodermis. 



The relations in the species of Equisetum may here be described according to Pfitzer^, 

 as being specially instructive for the arrangement of the endodermis, which is variable 

 even in closely allied plants. In the parenchymatous ground-mass of the internode there 

 is a ring of vascular bundles equal in number to the angles of the stem (comp. Chap. VIII). 

 In the foliage-stems of E. limosum and E. littorale an endodermal layer surrounds each 

 single bundle. In E. arvense, Telmateja, silvaticum, pratense, palustre (comp. below, 

 Chap. VIII), and scirpoides, this sheath is wanting round the single bundle, but sur- 

 rounds the whole ring externally, curving inwards between two bundles. Besides this 

 outer general sheath, there occurs in E. hiemale, trachyodon, ramosissimum, and varie- 

 gatum a similar inner one, i.e. one bordering the whole inner side of the ring of bundles. 

 In the rhizomes the same phenomena occur on the whole as in the foliage-stem; but in 

 the same species, as more minutely described by Pfitzer, the rhizome and foliage-stem 

 may be similar or dissimilar. Finally, at the points of transition between rhizome and 

 foliage-stems, Pfitzer often found in E. hiemale small strings of parenchyma 1-3 cells 

 thick, as seen in transverse section, which lay between two vascular bundles, and were 

 surrounded by an endodermal layer, the latter either arising as a protrusion from the 

 • general sheath, or having no connection with it. 



The cells of the endodermis (see Figs. 49 and 50) are nearly of the four-sided 

 prismatic form, very often flattened in the direction of the tangent of the part 

 enclosed by them, more or less elongated, with horizontal or oblique ends, and 

 connected uninterruptedly with one another along their radial lateral faces. Their 

 membrane is always delicate when differentiation of tissues begins, and often 

 throughout life it is smooth externally and internally, rarely it is delicately pitted ; 

 but the radial walls are characterised by a fine and usually irregular wavy transverse 

 folding, which is continued over the ends froma one radial wall to the other. Further, 

 the undulation extends, according to the special case, either over the whole surface, 

 or only over a band-like longitudinal strip of it. 



The wall of the cells is further characterised by suberisation, which appears 

 early, i. e. with the first differentiation of tissue : this always affects the undulated 

 part of the wall, and may also extend, according to the special case, in varying 

 degree over some or all of the other walls. This is the case in the majority 

 of Ferns : a good example of the localisation of the suberisation on the undu- 

 lated bands in the middle of the radial (cellulose) walls is supplied by the root 



* Von Kamienski, Vergleichende Anatomic cler Priraeln, /. c. 



^ Ueber d. Schutzscheide der deutschen Equiseteii, Pringsheini's Jahib. VI. 



