INTRODUCTION TO CRYPTOGAMIC BOTANY. 509 



form fruit is at once decisive ; and though the filmy, loosely- 

 cellular leaves of Hymeno'phyllum (Fig. 110, a) resemble 

 Symphyogyne, there is no resemblance in the fruit. These, in 

 fact, are mere cases of analogy, and deceptive only on super- 

 ficial examination. In a few cases only, as in Acrostichum, 

 the fruit is produced on the upper side ; but the structure in 

 these cases, and the whole character, are so decidedly the same, 

 that there is no difficulty. Indeed, in one or two very rare 

 instances, fruit is produced on the upper side in genera where 

 it is usually hypophyllous. Dr. Hooker has shown me, for 

 example, a specimen of Aspleniwm, Trichomanes, from 

 Genoa, in which there is a sorus on the upper surface ; and in 

 a late number of the Kew Garden Miscellany Sir W. J. 

 Hooker has figured a Fern from Ceylon, with the fruit on the 

 upper side.* In one or two genera, again, the sporangia are 

 wholly destitute of a ring, whether more or less complete ; but 

 in these cases the other characters are such as to remove all 

 doubt about affinity. The sori, moreover, are in normal cases 

 confined to the veins or veinlets, whether at some point in 

 their course or at the tip; but in a few genera the sori of neigh- 

 bouring veins unite, and extend from the vascular bundles to 

 the neighbouring parenchym, or the sporangia are scattered 

 indefinitely. 



571. The spores of Ferns, which are produced like those of 

 Muscales, by cell division within the sporangia, and are there- 

 fore unattached, are variously shaped, according as the separa- 

 tion in the mother-cell takes place at an earlier or later period, 

 and variously sculptured. They consist of two coats contain- 

 ing a grumous mass. On germination, the outer coat bursts, 



* This is figured under the name of Polypodium anomalum, of which 

 genus it has the characters. But Sir W. J. Hooker is almost convinced 

 that the plant is a mere monster of Polystichum vestitum. The tissue 

 is certainly much closer than in that species, as far as I can judge from 

 the comparison of sections of the leaves of two specimens only. There 

 is no doubt that the sori are really produced on the upper side, and 

 that the frond is not reversed like the leaves of Alstrcemeria or the 

 lacinife of Sckizxa, as the structure of the soriferous side is essentially 

 that of the upper and not of the under side. 



