316 H0FMEISTER, ON 



peared in some prothallia to be arranged in three rows. 

 Slender prothallia consist throughout, even in the cylin- 

 drical portion, of tissue homogeneous with that of the knob. 

 In thicker prothallia a string of cells in the axis of the 

 cylinder attains to double the length of the cells of the 

 peripheral tissue. The former contain only a few 

 amyloid granules ; the latter are quite filled Avith them. 

 Dichotomous prothallia were but rarely seen, and a repe- 

 tition of the division of one of the branches was of still rarer 

 occurrence. When in a normal position the apex of the 

 prothallium tends to grow to the surface of the ground. As 

 soon as it reaches the light it assumes a green colour, the 

 amyloid granules receiving a covering of chlorophyll. 

 The effect of light seems to be to limit the further growth 

 of the prothallium : the protruding apex either dies, or 

 becomes flattened, or divides into two or three small lobes, 

 which develope themselves no further. Antheridia and 

 archegonia are met with on the same prothallium without 

 any definite number or arrangement. They are either 

 altogether wanting on the knob, or are present in small 

 numbers at the base of the prolongation. They are always 

 plentiful upon the latter. Slender prothallia produce more 

 antheridia than archegonia : in vigorous prothallia the 

 archegonia are most numerous. The development of the 

 sexual organs progresses from the base of the prothallium 

 towards its apex. Their structure entirely resembles that 

 of the same organs in Botrychium. The youngest ob- 

 served embryos are ellipsoidal bodies consisting of few cells. 

 That end of the rudiment of the embryo which is turned 

 towards the apex of the prothallium forms the first leaf; the 

 opposite end forms the first adventitious root. Both cause 

 an expansion of the surrounding tissue ; the leaf makes itself 

 a passage for a longer or shorter distance into this tissue, 

 sometimes penetrating, with a turn downwards, as far as the 

 knob, and growing through it. After its egress the leaf is 

 enclosed by the drawn-out portion of the prothallium. Its 

 fore-surface is turned towards the apex of the central cell of 

 the archegonium, a circumstance in which it agrees with 

 Botrychium, and differs from the Polypodiacese and Rhizo- 

 carpeee. The first root, as soon as it is formed, bends out- 



