78 EQUISETACEiE. 



species of Equiseta are dioecious, the female prothallium being 

 larger than the male. In the antheridia are developed a very 

 large number of motile antherozoids ; in the archegonium is a 

 single central cell, containing an oosphere, which after impregna- 

 tion develops gradually into the young plant. The alternation of 

 generations is therefore precisely similar to that of ferns. The 

 Equisetacese are also propagated in a vegetative, non-sexual 

 manner, by means of subterranean stolons and tubers. "The 

 affinities of these plants," as Berkeley observes, " are quite clear 

 since the discovery of the extreme similarity of the mode of 

 development with that of ferns. The archegonia and spermato- 

 gonia, with their spermatozoids, are, in fact, almost identical. 

 The resemblance to Marchantiacece 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 archegonia produce 

 merely a sporangium \ in Equisetacece, a new plant. The resem- 

 blance between these plants, again, and such Phsenogams as 

 Ephedra and Casuaritia is very striking, but it is, after all, merely 

 analogical. " The superior development of the cellular tissue 

 indicates a higher type than that of ferns, and if the nobler forms 

 of these are objected, we have but to point to extinct Eguisetacece.'" 

 A very interesting plant, which has no affinity with Equiseta, 

 although both its botanical and English name would seem to 

 point to a relationship, is Hipp^iris vulgaris, L., the Mare's Tail. 

 It grows frequently in close proximity to E. ntaxit?tum. I have 

 gathered specimens of both, growing within a foot or so of each 

 other, in the neighbourhood of this city (Bath). This plant seems 

 at one time to have been classed with Horsetails. This was 

 before compound microscopes were regarded as essential to the 

 study of botany. The application of the microscope to a trans- 

 verse section of the stem makes it manifest that the Mare's tail is 

 an exogenous plant. Further examination shows that it is not a 

 cryptogamic, but a flowering plant, for the flowers arise from the 

 axils of the leaves. I have made a sketch of a transverse 

 section of the plant, to enable you to compare it (PI. X., Fig. 4) 

 with one of E. arvense, L. (PI. X., Fig. 5). If I am open to 

 the charge of wandering away from the subject of my paper, I 

 must plead in extenuation that I have done so for the purpose of 



