16 
INTRODUCTION. 
same time, and in a healthy condition form circular patches, a quarter to half an 
inch in diameter, composed of four or six vivid green lobes, looking like a patch 
of young Liverworts. The archegonia are produced on the front margins of the lobes 
of the prothallium, but by the thickening of the tissue beneath soon appear to be 
upon the upper surface. They essentially resemble those of the Ferns, and are in like 
manner fertilized by active ciliated spiral filaments discharged from the antheridia ; 
here, however, often five or six are fertilized on the same prothallium. The germinal 
vesicles in the interior of the archegonia then at once commence their development, 
and break forth as rudimentary stems with imperfect sheaths (representing the 
leaves) and root-fibres. The first bud at the top of the young plant is usually 
little developed, but lateral buds arise in the axils of the sheath-scales, which 
form horizontal branches, and thus produce the ramified subterraneous rootstock 
characteristic of these plants. The sheaths of the young stems have very few 
teeth, and these increase in number as the stems gather strength and acquire 
larger dimensions (similar to the gradual acquisition of the true form of the leaf 
in the Ferns). The development of the Equiseta from their spores takes place 
very rapidly ; those of E. variegation sown in the beginning of May produced 
leafy plants upon the female prothallia by the middle of July.* — A. II.] 
DISTRIBUTION. — “Nearly equal in number with the Lycopodiaceai, the 
Plants included under this order contrast against them in their distribution. 
Whilst the former are described in general terms as plants of the moors and 
mountains, the Equisetaceae belong more especially to marshes, fields, and 
woods. Both orders, or genera, are alike widely distributed through Britain ; 
but whilst the Lycopodiums prevail high on the mountains, the Equisetuins 
are more abundantly bestowed upon the lower grounds, or the plains and valleys ; 
the latter also evince more of a maritime, or even littoral tendency than the 
Lycopodiums, being often seen in abundance on and near the sea-shore.”— 
Mr. Watson’s MS. 
USES.— They are harmless to cattle, but refused on account of their husky, 
rigid texture. They are useless as medicines, but employed in the arts ; their 
siliceous cuticle rendering them valuable as polishing substances for marble, wood, 
ivory, and even metals. 
ISOETACEiE. 
( Containing Isoctes only.) 
Lycopodiacea, Lind., Decan., Brongn. 
Marsileacea, Hook. 
Miscellanea, Part of Rhizosperma, Rhizopterides, 
Hydropterides, &c. 
STRUCT URE. The genus Tsoetcs (see the woodcut illustrating this genus) has 
More minute details maybe found in the following memoirs (in German): Milde, 
‘ Ueber Equiseten, Linna-a, 1850; W. Hofmeister, * Verglelchentie Untersuchungen hohoren 
Kryptogamen, Leipsic, 1851 ; and ‘ BeitrHgezur Kenutncis der Gefarskryptogamen’ (Trans, 
of the Royal Society of Saxony, vol.iv).— A. tl. 
