ido VASCULAR CRYPTOGAMS 



morphosed portion of a leaf. They are buried, in an early stage, in 

 parenchyme, which ultimately becomes entirely absorbed, and which is 

 traversed by ' vascular ' bundles anastomosing into long meshes. The 

 sporanges require an entire year for their complete development. They 

 have no annulus, and dehisce vertically from unequal tension of the 

 epidermal and hypodermal layers of cells. In the formation of the 

 spores each mother-cell divides into four ' special mother-cells,' with 

 very thin cell-walls ; the protoplasm in each of these becomes invested 

 with a new and firmer cell-wall, and the spores are thus completely 

 formed, and are ultimately set free by the absorption of the walls both 

 of the special mother-cells and of the original spore-mother-cells. The 

 spores are nearly cubical ; the exospore is strongly cuticularised, and is 

 furnished with prominent knobs and ridge. 



Vegetative propagation is known to take place only by means of 

 adventitious buds produced on the roots. 



The Ophioglossaceae include only a very small number of species, 

 comprised in the genera Ophioglossum (L.), Botrychium (Sw.), and 

 Helminthostachys (Kaulf.), spread over the whole globe. They are small 

 plants, dying down each year, only a few species attaining the height of 

 more than a foot, with a single or only a very few coriaceous leaves, and 

 a conspicuous ' fructification,' which is simple and spicate in Ophio- 

 glossum and Helminthostachys, branched and paniculate in Botrychium. 

 They are of no known economic value. They are represented in our 

 English flora by the * adder's-tongue ' (Ophioglossum vulgatum, L.) and 

 ' moonwort ' (Botrychium Lunaria, Sw.). 



LITERATURE. 



Mettenius Filices Hort. Bot. Lipsiensis, 1856. 

 Hofmeister Abhandl. Sachs. Gesell. Wissenschaften, 1857. 

 Holle Bot. Zeit, 1875, pp. 241 et seq. 



Prantl Ber. Deutsch. Bot. Gesell., 1883, pp. 155 and 348 ; and Jahrb. Bot. Gart. 

 Berlin, 1884. 



Class VI. Equisetacese. 



The Equisetacese or Horsetails are a very small group of plants, con- 

 sisting only of a small number of species, arranged in a single genus, 

 of remarkably uniform and peculiar habit. The aerial stems, which are 

 invariably erect or ascending, arise from a creeping underground rhizome, 

 and are characterised by their perfect multilateral symmetry and verticil- 

 late branching. The ascending stem is always elongated and slender, 

 fluted with longitudinal furrows and ridges, and is remarkable for the 



