ZOOLOGY AND BOTANY, MICROSCOPY, ETC, 77 



others are usually formed, but if not a few others are subsequently 

 developed. When quite mature the part of the prothallium which 

 projects outside the spore is nearly hemispherical, and three obscure 

 wings are produced by three longitudinal furrows. The cells contain 

 chlorophyll. 



The position of the oosphere with respect to the neck of the 

 archegonium probably corresponds to that in Salvinia. After fertiliza- 

 tion it is divided by the first oblique division-wall into a smaller upper 

 cell facing the neck of the archegonium, and a somewhat larger lower 

 cell filled with coarsely granular protoplasm. By successive walls 

 vertical to one another and to the first division-wall, and parallel to 

 its longitudinal axis, the embryo is then divided into octants. In each 

 octant a wall next appears parallel to the first division- wall ; and the 

 entire embryo then consists of 16 cells, arranged in four parallel 

 rows. 



The four cells which lie at the upper pole are the rudiment of the 

 foot. Of the four lowermost cells one is the origin of the apex of the 

 stem, another developes into an organ resembling the first leaves, the 

 two others are together the rudiment of the scutellum. In its sub- 

 sequent growth the young apex of the stem follows the ordinary laws ; 

 only the bud is at first straight, and the characteristic curving upward 

 of the cone of growth is a subsequent phenomenon. The leaves first 

 produced are strongly concave, and, in contrast to the later ones, are 

 not lobed. Some of the hairs which mark the upper side of the apex 

 of the stem are formed at the same time as the first leaf. The scu- 

 tellum originally encloses the bud as a crescent-shaped growth, the 

 margins of which gradually approach until it encloses it like a 

 sheath. The leaf-like organ resulting from the second cell of the 

 lower pole of the embryo is at first, like the scutellum, independent 

 of the apex of the stem, and morphologically equivalent to it. Neither 

 can therefore accurately be termed a leaf. The first vascular bundle 

 of the plant is formed at an early period by tangential walls in the 

 eight cells which compose the centre of the embryo. 



After fertilization the embryo turns, as in Salvinia, within the 

 archegonium, so that the apex of the stem is turned towards that of 

 the prothallium. The embryo breaks through the prothallium near 

 the archegonium, and the prothallium then surrounds the foot of the 

 embryo like a cup, carrying the withered archegonium on its dorsal 

 side behind the scutellum. 



To prepare for fertilization, the massulse of the microsporangia, 

 with their anchor-shaped glochidia, fix themselves in large numbers 

 to the under epispore of the macrospores which are floating on the 

 surface of the water. The central fibrous portion of the floating 

 apparatus is perforated by a narrow canal, through which the anthe- 

 rozoids probably reach the archegonium. By their subsequent growth 

 the prothalliiim, and later also the embryo, force themselves into this 

 canal, and increase its size. By this means the three floating bodies 

 are displaced from their original position, and finally stand at a right- 

 angle from the macrospore. The indusium which covers the floating 

 apparatus in the form of a brown cup is at the same time pushed 



