1 6 WAYSIDE AND WOODLAND FERNS. 



where they are further sheltered from strong top-light by pro- 

 jecting masses of rock, and the exposed thick root-limbs of the 

 trees, you may find the Tunbridge Filmy-ferns growing not as 

 individuals but as a tapestry of associated hundreds. 



The fronds vary from an inch to three inches in length. In 

 exceptional cases and in cultivation they may exceed the larger 

 measurement, but as a rule the smaller size is the prevailing 

 one. The most conspicuous feature of the somewhat egg- 

 shaped, dark-green frond is the midrib and its alternate but 

 nearly opposite side branches. These are dark and of firm 

 texture, and are winged on either side with a very thin and 

 pellucid membrane, of such delicacy that it readily shrivels on 

 exposure to a dry atmosphere. This membrane is without the 

 stomata or breathing pores usual in fronds and leaves, the 

 material being so thin that gases can be absorbed through 

 the cell-walls. It extends down each side of the rachis and 

 some distance down the stipes. Each of the pinnae or wings is 

 cut into several narrow lobes with spine-like teeth along their 

 margins. In the angles between the upper pinnae and the mid- 

 rib will be found a slightly stalked urn-shaped brown body 

 consisting of two valves whose upper edges are toothed. These 

 toothed edges are an important character, helping to distinguish 

 this species from the next. The spores are ripe in June or July. 



On opening one of these urns we shall find within it a short 

 central column on which are crowded a number of spore cap- 

 sules, each with a broad elastic ring (running obliquely round 

 the capsule) whose rupture disperses the contained spores. It 

 is interesting to note, by the way, that the spore in this genus 

 on germinating does not give rise to the heart-shaped, scale-like 

 prothallium already mentioned as the prevailing type among 

 ferns. There is a prothallium, of course, but in the Filmy 

 Ferns it is long and slender, like the first shoot from a moss- 

 spore. It may be remarked of both species of Filmy Ferns, that 

 all the published drawings we have seen our own excepted 



