PRIMARY PARENCHVMA. SHEATHS. 415 



Lactuca virosa, and the bundle-sheath in the stem of Ranunculus fluitans ; comp. the 

 explanation of Fig. 153, p. 332. The two forms of sheath may mutually replace 

 one another in the same region, according to the* species; the plerome-sheath, for 

 example, appears in the hypocotyledonary stem of Helianthus annuus as a starch- 

 layer, in that of Tagetes patula as an exquisite endodermis. The thin vascular 

 bundles, especially the bundle-ends of the foliar expansions, are usually surrounded 

 by a parenchymatous sheath different from the two distinguished above, and con- 

 sisting of elongated elements passing over gradually into the epithema at the peri- 

 pheral ends. (Comp. Sect. 1 1 1 .) 



■ The sheath of single trunks of vascular bundles appears in the form of an 

 endodermis, around the axial bundles of roots and of most stems which have them, 

 around the bundles of almost all Ferns, and those in the stem and leaves of certain 

 Phanerogamic plants. To the cases and descriptions already given in Sect. 27, and 

 Chap. VIII, we have here to add the bundles of the leaves of Hottonia, Cortusa, 

 Dodecatheon, Cyclamen, Soldanella, Trientalis'; those of the stem of Caltha 

 palustris, which, according to Russow, are surrounded by a wholly or partially 

 sclerotic . endodermis ; and especially, according to the statements of the latter' 

 author", and of Schwendener', the bundle-trunks in the leaves of Cyperaceae, 

 Juncacese, and Grasses, in which the endodermis, which usually soon becomes 

 thickened by sclerosis, lies between the vascular bundle and the strand of scle- 

 renchyma ensheathing it. 



An endodermis ensheathing the whole ring of bundles is present both on the 

 cortical and the medullary side of the latter, in the species of Equisetum enumerated 

 at p. 122. In other species of this genus, e.g. E. palustre. Fig. 149, p. 329, it only 

 extends around the cortical side of the ring of bundles, and the same is the case 

 with the endodermal plerome-sheath which surrounds the ring or cylinder of the stems 

 of Phanerogams. As selected examples for the occurrence of this, have already 

 been mentioned (p. 121) the stems of Cobgea, Tagetes, Lobelia spec, the rhizomes of 

 Scitaminese, Cyperacese, &c. According to the investigations of Dr. v. Kamienski, which 

 have been privately communicated to me, numerous Dicotyledons are to be added 

 to this list ; Linaria, Pedicularis spec, Camelina, Capsella, Atriplex patula. Euphorbia 

 spec, Mercurialis, all Primulacese ; and according to Vochting ' the Melastomaceae. 

 Further investigations will have to decide how far the endodermal structure of the 

 layer surrounding the plerome and vascular bundles in stems and leaves generally 

 is of usual occurrence. 



The plerome-sheath is developed in the form of the starch-ring or starch-layer^ in 

 the stem of most Dicotyledons, as far as can be decided from the existing investigations. 

 Sachs, for example, finds this to be the case in seedlings, especially in the hypo- 

 cotyledonary stem of Helianthus annuus, Cucurbita, Phaseolus, Iberis, Raphanus, 

 Prunus, Amygdalus, Convolvulus, Quercus, Acer, Ricinus, (comp. Fig. 154, p. 333), 

 in the stolons of the potato, and in the mature stem of Dahlia and Ricinus. The starch- 

 layer is in these cases either uniformly developed around the whole ring of bundles, 



Kamienski, private communication. " Vergl. Unters. pp. 169, 170. 



Das mechan. System, p. 17. ' I.e.; compare p. 259. 



= Sachs, Botan. Zeitg. 1859, P' '77' Taf. VIII. IX; Pringslieim's Jahrb. III. p. 194. 



