278 PRIMARY ARRANGEMENT OF TISSUES. 



HippurisS Callitriche^ Myriophyllum ', Ceratophyllum ', probably Utricularia, and 

 the non-aquatic genus of Piperace» Verhuellia ° : of Monocotyledons, the Hydrille^, 

 Elodea canadensis, and Hydrilla verticillata ^ ; Najas'', and the rhizomes of the root- 

 less Orchids which grow in humus, Epipogon Gmelini, and Corallorrhiza innata ". In 

 Corallorrhiza and the stolons of Epipogon a branch passes from the axile bundle 

 into each of the biseriate scale-leaves : in the coral-like rhizome of Epipogon, which 

 has short internodes, the branches which pass to the leaves are absent, according to 

 Reinke. 



According to the structure and development of the bundle the following plants 

 may be placed in the third intermediate category ; perhaps Myriophyllum, Hippuris, 

 and Elatine Alsinastrum : further the larger Potamogetons belong to this series : 

 their original arrangement of cauline bundles and bundles of the trace has been 

 described above on p. 272. In the series of described' species of this genus, and of 

 allied forms such as Zannichellia and Althenia, with which Elodea, Najas, &c. are 

 also connected, there are to be found all stages of simplification of composition (and 

 of structure) of the axile bundle : leaf-traces consisting of one or more bundles, 

 running side by side with cauline bundles through the internodes, are found in the 

 stronger, more leafy forms, at one end of the series, while at the other a single cauline 

 bundle is present, which unites at the node with the bundles from the leaves. 



VII. Fern-like Plants. 



Sect. 73. In the young seedlings of all the investigated forms of this series the 

 bundle-system of the stem is a sympodium of leaf-traces consisting of one bundle 

 (which with the exception of Equisetum developes in an acropetal direction). The 

 first bundle, which usually ends blind in the foot of the embryo, curves after a very 

 short course through the stem into the first leaf; from the point of curvature the 

 development of a bundle, which runs out into the second leaf, begins. In the case 

 of the subsequent leaves the same conditions prevail. 



In Isoetes, Equisetum, and Osmundaceae, this construction of the bundle-system 

 out of distinct leaf-traces is permanent even in the mature stem. The same holds 

 perhaps for many Ferns with a simple axile bundle. In the Lycopodiums, and 

 Selaginellas, the axile bundle which traverses the stem, or the two or more bundles 



1 Nageli, Beitr. I.e. p. 56.— Sanio, Botan. Zeitg. 1865, p. 191. 



^ Nageli, /. c. — Hegelmaier, Monogr. d. Gattung Callitriche. Idem in Martins, Flora Brasil. 

 fasc. 67. 



° Vbchting, Zur Histologic u. Entwicklungsgeschichte v. Myriophyllum, Acta Acad. Leopold. 

 XXXVI (1872). 



* Schleiden, Beitr. p. 316.— Unger, Anatom. und Physiol. 198. — Sanio, Botan. Zeitg. i86j, 

 p. 192. 



° Schmitz, Flora, 1872. 



" Caspary, in Pringsheim's Jahrb. I. Idem, Verhandl. d. Nalurforscher u. Aerzte z. Konigs- 

 berg, 18S0. 



' Compare Magnus, Beitr. z. Kenntniss d. Gattg. Najas, p. 48. 



' Irmisch, Beitr. z. Morphologic und Biologic d. Orchideen.— Schacht, Pflanzenzelle, p. 268. 

 Idem, Lehrbuch, II. p. 21.— Reinke, in Flora, 1873. 



