350 



BOTANY. 



Fig. 239.— Plant of An- 

 thoe&ros kevis. K, on the 

 right, sporogonia un- 

 opened ; K, on tlie left, 

 Fporoffonia opened. — After 

 Prantl. 



takes place simply by the decay of the sporogonium ; in 

 Anthoceros the long sporogonium splits 

 vertically into two long valves (Pig. 

 339), while in the greater part of the 

 class it splits regularly 

 into a definite number 

 (four to six) of recurv- 

 ing segments ; in the 

 latter the elaters, which 

 are present, doubtless 

 aid in setting the 

 spores free. The struc- 

 ture and development of the elaters are 

 shown in Fig. 240. 



The following are tlie principal orders of the 

 Hepaticse : 



Order Ricciacese. — Consisting of terrestrial or 

 aquatic annual plants of small size ; the plant- 

 body is a dichotomously branched thalloid stem, 

 which beard a row of scale-like leaves upon the 

 under side. The sexual organs occur singly on the 

 upper side of the stem, and the sessile, spherical 

 sporogonia (capsules) are immersed in it or sessile 

 upon it ; the capsule breaks irregularly upon the 

 decay of its walls ; and there are neither perianth 

 nor elaters. 



Order Antliocerotese. — Terrestrial annual 

 plants with an irregularly branched thallus. The 

 sexual organs are inihedded in the upper surface 

 of the f loiid, and are of very simple structure ; the 

 sporogonia are long and narrow, and dehisce by 

 splitting into two valves ; perianth none ; and the 

 elaters, when present, imperfect and rudimentary. 



Order Marchantiacese. — Terrestrial perennial 

 plants, with a thick, creeping, and dichotomously 

 branched stem, furnished beneath with numerous 

 scale-like leaves and root-hairs ; above, the stem is 

 provided with a well-developed epidermis, and pe- 

 culiar stomata of a complex structure, communi- ii°^ii)'|"broken°awaT 

 eating with lozenge-shaped cavities (Figs. 78 and A., A, are matiirft 

 79, pp. 91-3). The sexual organs are developed on ^^°;^ Le^MlmitaS 

 special erect branches, and they may occur on the Decaisne. 

 same, oi' on distinct plants ; the sterile or antheridial branches, which. 



Fig. 24(1.— Two ela- 

 ters in different stages, 

 of development. The 

 one on the left is seen 

 to bean elongated cell 

 with no trace as yet 

 of the spiral thicken- 

 ing of its wall. By its 

 side are several young 

 spores. Theelateron 

 the right is mature. It 

 is composed of the spi- 

 rally thickened por- 

 tions of the wall, the 



