550 INTRODUCTION TO CEYPTOGAMIC BOTANY. 



from the reniform Marchantioid expansion of the young plants 

 of that important order. As in ferns, archegonia and sperma- 

 togonia are formed upon the prothallus, and the spermatozoids, 

 as in that order, are fringed with abundant ciHa. The arche- 

 gonia give rise equally to the perfect plant, which throws out 

 a rhizoma from which new shoots are produced. The fruit is 

 a little strobilus, terminating the stem or main branches, and 

 consists of peltate scales, supporting a whorl of sporangia, 

 arranged vertically round the short stem, with their base 

 attached to the scale and the upper end free. The walls are 

 composed of beautifully spiral tissue, and the spores arise by 

 cell-division, each spore being covered with a separable mem- 

 brane, which ultimately splits in a spiral direction, so as to form 

 two bands with clavate apices, which are attached by the 

 middle, so as to look like four stamens. The structure of the 

 rhizoma is very different from that of ferns. In an early stage 

 it consists of a central column of cellular tissue, sending off 

 about eight radiating plates, which connect it with an external 

 cylinder of the same tissue, and opposite to each of which 

 there is in the central column a vascular bundle, consisting of 

 annular vessels passing into spiral. At a later period tissue 

 grows from the walls into the cavities in such wise that they 

 are more or less perfectly obliterated. More abundant cavities 

 exist in the fruit-bearing stems, with various modifications of 

 the component tissue. Annular vessels, however, predominate, 

 as scalariform vessels do in ferns. The cells of the sporangia 

 are remarkable for the beautifully developed spiral formed by 

 their inner coat. The cuticle is furnished with stomates. 



627. The affinities of these plants are quite clear since the 

 discovery of the extreme similarity of the mode of development 

 with that of ferns. The archegonia and spermatogonia, with 

 their spermatozoids, are, in fact, almost identical. The resem- 

 blance to Alarchantiacece in the fruit is striking, but this is 

 rather one of analogy than of affinity, as the results of impreg- 

 nation are so different. In Marchantiacece the archeo-onia 

 produce merely a sporangium, in Equisetacece a new plant. 

 The resemblance between these plants, again, and such Phseno- 

 ganis as Ephedra and Gasuarina is very striking, but it is. 



