196 NATURAL SCIENCE. March. 



circular mouth, bounded by a strong rim or collar, opening on the side 

 next to the stem. Direct entrance is impossible, as the mouth is 

 closed within by the depressed tissue of the circular area of the mouth, 

 and entrance can only be effected by a passage downwards between 

 the two flaps of the valve. One of these flaps is rigid, and exactly 

 hke the rest of the foliage in texture, but the other consists of thin- 

 walled, empty, and dead cells; the latter forms the "clapper," and by 

 its easy movement the opening and closing of the valve is effected. 

 The shoots bend outward from the tree to which they are attached 

 and grow vertically upward. The provision for the conduction of 

 water into the auricle is remarkably perfect. " The upper lobe is 

 well adapted, both by its shell-like form and its position on the upright 

 stem, for catching and holding water, which, owing to its oblique 

 position, will naturally flow toward the auricle. It is prevented from 

 running off by the lower edge being strongly incurved, thus forming a 

 channel in which the water may collect, and leading to the mouth of 

 the auricle. The curved edge of the lobe is continued by a projection 

 into the mouth of the auricle, the upper edge of which is raised to 

 prevent the water escaping at the junction of the two members, while 

 a depression below^ forms a channel which ensures the entrance of the 

 water into the auricle" (2). How effective a water collector this plant 

 is may be readily seen in the epiphytism it engenders, a variety of 

 small plants and animals being commonly found in the sac, while a 

 species of Frullaiiia was in some cases so closely applied to the 

 shoots as to be invisible except on close examination. 



There is yet another means whereby water is collected and held, 

 viz., the perianth or colesula. This is a more or less cylindrical sac, 

 which develops around the archegonia, and after fertilisation elongates 

 considerably, and encloses the developing sporogonium. As it stands 

 vertically, and is in most cases much larger than is necessary to cover 

 the young sporogonium, it will doubtless catch more or less water, 

 which in those having a contracted mouth will be held with great 

 tenacity. But in a number of species the colesulae are mostly, and 

 sometimes entirely, barren, the archegonia being in some cases 

 entirely suppressed. These barren colesulae are occasionally pro- 

 duced in immense numbers, as in Physioiinm acinosmn, where they 

 form the main mass of the plant, the stem and leaves being small and 

 comparatively insignificant ; and that they function as water sacs is 

 evident from the fact that water can be wrung from the fresh plant 

 after weeks of rainless weather in a dry locality. There is, however, 

 a disadvantage in this habit, as seeds are enabled to germinate in the 

 vicinity of the liverwort, and the seedlings send their roots into the 

 colesulae and rob the plant. But the advantage to the "epiphyte" 

 is very great, as the plantlets, which otherwise might not have 

 germinated at all, have now become independent. 



Another interesting point which has been recently brought to light 

 is concerned in the moistening of the apex. The mucilaginous papilla 



