Exogenous Seeds and Fern Spores. 335 



be seen on all markings, such as seen in Plate (Figs. 1 

 to 7) . What are these markings ? 



If a spore be examined when young and transparent (Fig. 8, 

 Platy cerium alcycome), it will be noticed that there is an 

 outer covering and an inner lining membrane filled with clear 

 homogeneous matter, and invariably, near the marking above 

 named, a compound body in a sac ; attached to the sides of 

 which, proceeding from the marking to the body, are two 

 small processes if the body be in the centre of the marking, 

 but one, if it be to the side. If the mature spore of the same 

 plant be examined, it will be found, as at Fig. 7, filled with a 

 mass of yellow refractive globules, and the nucleus will with 

 difficulty be made out ; but if some reagents, such as glycerine, 

 be added, the globules will become transparent, and the 

 nucleus revealed again. These globules are the homogeneous 

 matter before named, plus other matter imbibed. If a mature 

 spore be grown and watched from time to time, the following re- 

 sults : — The spore swells, at the marking before named a peculiar 

 body appears (e, Fig. 9). This pushes its way through the 

 marking, as seen by the dotted lines, and so the cell is 

 ruptured. This marking proves itself to be a vaginal opening, 

 or, in other words, a foramen (p), and the body which has pushed 

 out, a radix. While this change has been going on, a corres- 

 ponding alteration has ensued within the spore. At the 

 upper part a cluster (a) of green bodies has appeared precisely 

 similar to those seen afterwards in all the cells of the pro- 

 thallium, while the globules of matter have shrunk into a mass (e) 

 not large enough now to fill the cell (b) . Meanwhile the cells at 

 a have constituted themselves into a new cell (c), excluding 

 B; c takes another cell (d), and this again another, and so on 

 till a body of the form of Fig. 13 is formed, which is called 

 the prothallium. While A has been undergoing these changes, 

 b's matter has wasted entirely away ; a few cells, such as seen 

 in a, are within it, but its future destiny is not absolutely 

 traced. 



For convenience I will name all these described parts. The 

 spore is a nucleus with a covering ; it contains a germinal 

 vesicle in a sac. The opening in the spore covering is the 

 foramen. When the spore grows, the radix forces open the 

 foramen, while the primary germ has been undergoing a 

 change. This reads very like the description of a seed; 

 and the similitude does not merely extend to appearance, but 

 the functions of both are alike. The only difficulty is in the 

 prothallium, which appears, at first sight, to have no analogy 

 in the seed, though, in fact, the cotyledons in the mustard 

 and the prothallium in the fern are identical, answering the 

 purpose of developing the plumule. I have hitherto, as far as 



