May, 1902.] 



KNOWLEDGE 



113 



of some twent}- axes attached to a central float. There seema 

 to us a lack of the personal element, or of appeal to the gi'eat 

 workers of the past century, such as often imjiarts life to a 

 description, and captures the interest of the beginner ; but 

 Professor Biighaui's work, utilised by an inspiring teacher, will at 

 least convey no false impressions. In saying this, we pas.s over the 

 old old statement on p. 97 that rnclir.i inoul'iimi-e.'< were so called 

 from their resemblance to a flock of sheep, for here our author 

 has the best of company. l)e Saussure was in reality struck by 

 the resemblance of these rounded rocks to the mammillations of 

 a fleece or wig. Probably in his desire to be popular. Professor 

 Brigham sjieaks of the "Irish Elk '' and maintains on p. 388 the 

 familiar distinction between Goniatite, Ceratite, and Ammonite, 

 an arrangement that gives Cerotites undue importance as a 

 group-term etiuivalent to all the other Triassic Ammonites. 

 Our author, like those before the days of Alpine exploration, 

 ignores the Triassic Ammonites altogether. 



A ^lip that seems worth connecting occurs on p. 197, where 

 gypsum is spoken of as " the only important rock-forming com- 

 pound of suljihur," "p3'rites'' — which certainly should be 

 " pyrite' or " iron pvTites" — being given later. The composition 

 of gypsum is not stated. Moreover, were crinoids (p. 3-5) so 

 named " from their likeness to a lily ' V On p. 55, the odd- 

 looking technical word " talus " is usefully connected with " an 

 ankle'' ; it may be well to note that the Low Latin form 

 liiliitinit was used also for a ])rojection, and probablj' gave rise 

 to the term " talus '' in engineering and geology. 



Altogether, for American readers, Professor Brigham's work 

 is concise and useful, though it cannot be regarded as a con- 

 tribution to knowledge. 



STUDIES IN THE BRITISH FLORA. 



By R. Lloyd Praeger, b.a. 



III.— FERNS. 

 The Fcrus whose cool greeu fronds peep at us from the 

 hedgerows or cluster iu shady <fleus aud on damp mouutaiii- 

 sides are au iuterestiuy race of plauts, aud hii,'h favourites 

 with all nature-lovers. The differences which separate 

 them from the Flowering Plants and place them, with their 

 allies the Horsetails aud Club-mosses, at the head of the 

 vast army of Cryptogams or Flowerless Plants, consist 

 chiefly in the lower type of the asexual generation (what 

 we know as the plant) and the prolongatlou and indepen- 

 dence of the sexual generation. In au ordinary Flowering 

 Plant, too, the pause iu vegetative growth, when the 

 individual gives rise by means of the dissemination of seed 

 to a number of new individuals, takes place after fertiliza- 

 tion has been effected by the union of male and female 

 elements in the flower. When the seed germicates, no 

 cessation of vegetative life takes place until seed has been 

 again formed subsequent to flowering. In the Ferns, 

 on the other hand, the formation of " seed " aud dis- 

 semination take place hefuie the production of the male 

 and female elements. The seed or spore grows into a 



Fio. 1.— St'otioii through a very ycMiiii; Feru. 1', the prutiial- 

 liiini, with root-hairs on under side. F, foot of .young fern-plant, 

 embedded in the hollow of the archegonium. R, first root, and 

 Fr, first frond, of young fern-plant. Much enlarged. 



pioihalllum — usually a minute green heart-shaped pros- 

 trate leaf-like growth, on the under side of which the 

 male and female organs (anlln'ridia and archegonia) are 

 developed. The autheridia liberate a number of anthcro- 

 zoiih, tinv coiled motile bodies, which twist about and 



swim in the surrounding moisture, aud eventually fertilize 

 the archegonium by fusion with the ovum, or egg-cell, 

 which it contains. Fertilization being effected, the growth 

 of the new plant from the ovum commences at once. The 

 j)rothallium fades away, and the young fern increases iu 

 size, and generally lives for many years, producing on the 

 under side of its greeu fronds abuu<lauceof spores, capable 

 of again giving rise to the prothallium form. In other 

 words, tliere is thus in Perns a tlislinct alternation of 



Fia 2. — Young Fern older than in Fig. 1, showing 

 prothallium (under side), and first root and frond of 

 i'ei-u-phint. Much enlarged. 



generations. The oophyie is a minute aud normally short- 

 lived plant, while the spuroiihytc usually lives for many 

 years, and sometimes, as iu the Tree ferns, attains very 

 large dimensions. It will be noted that when a " fern " 

 is spoken of, it is the asexual generation, or sporophyte, 

 that is always meaut. The non-botanical reader is asked 

 to carefully note the incidents, as briefly sketched, of this 

 life-cycle, in view of certain remarkable departures from it 

 which will be considered towards the end of the present 

 article. 



So much for the life-history of Ferns. As regards their 

 history on this earth, I'erus jiresent an immensely long 

 lineage, longer by far than the oldest of the Flowering 

 Plants. They make their first appearance as fossils iu 

 Devonian rocks, amid their allies the Horsetails ; and in 

 the hot steaming forests of the Carboniferous Period, 

 whose remains form our Coal-measures, they attained a 

 wealth of variety and luxuriance that in the millions of 

 years that succeeded has never again been equalled. Still, 

 they form au important portion of the present vegetation 

 of the globe, numbering, at a low computation, three 

 thousand species, belonging to about sixty genera. 

 Attaining their fullest development in the hot damjj 

 Carboniferous forests, they have ever since maintained 

 their preference for heat aud moisture. The vast bulk of 

 the three thousand existing sjiecies cling to the Tropics, 

 and among the forty- seven species which are found in our 

 Islands, hardly one but seeks a damp and shady situation. 

 To revert to a term used in my last article, Ferns are 

 essentially hugropkiles — moisture-lovers — and the student 

 of botanical geography will note how they increase iu 

 number as one passes from dry to wet regions — as one 

 leaves the " Germanic " flora of East Anglia, for instance, 

 for the " Atlantic " flora of Wales. Not one of our Ferns 



