164 



-KNOWLEDGE 



[July, 1902. 



H. — DiMiNPTioN OK Soft Parts. — Tho varieties wbicli 

 foiiic under this licad liiive little of the interest or bcuuty 

 tliul pertains to those of the last. Mo.st of them exhibit 

 in irref,'iil;ir diminution or sujiprcssion of the jiinnuloH, 

 the niiilribs of which being sometimes all that remains, 

 standiu},' out like bristles. Sometimes the ])innie or 

 pinnules are symmetrically abbroviateil, with a round<'d 

 margin, as in P. amiulare, var. rotuiuhitum, or a frilled 

 margin, as in Mr. Druery's delightful little Blechnum 

 Spicant, var. concinnuin. 



I — Subdivision. — Almost every Fern varies at least 

 slightly as regards the amount of subdivision which its 

 fronds display. This applies particularly to the species with 

 much divided fronds, such as the Lady Fern and Soft Shield 

 Fern, which may be bipinnato, or sub-tripiunate, or 

 tripinnate, or sub-quadripinnate. according to the size and 

 development of the plant. But this normal variation is 

 ■wholly eclipsed by the surprising abnormal development 

 which not inifrequently displays itself. A few of the more 

 modest variations of this class have, apparently merely on 

 account of frequent occurrence, been admitted as genuine 

 varieties into the British flora. Thus, the fronds of the 

 Scale Feni are normally merely deeply lobed, but when 

 growing strongly the lobes are frequently themselves 

 lobed, and become var. crenatum. Similarly with Asjjle- 

 iiium Adiantum nigrum, var. acutuni, a well-marked and 

 wide-ranging dissected form, while in Polypodinm vnlgare 

 not only is var. serratum admitted, the analogue of which 

 occurs in almost every British fern, but also the plumose 

 form, var. cambricum, In Polystichum angidare one notable 

 group of varieties comes under this class — the proliferum 

 section. The first example of this group was found by 

 Choule, one of the Kew gardeners, over fifty years ago, 

 and was at the time considered to be a foreign fern, so 

 peculiar and well marked were its characters. The frond 

 was elongate, with a very short foot-stalk, tapering up- 

 wards from the lowest pair of pinnae ; the pinnules very 

 long and cut into narrow acute pinnules ; and the midrib 

 bore buds which developed into young plants long before 

 the frond faded. Fig. 5 contrasts a normal pinna with 



Fio. 5. — Pinnae of Poli/stickum annulare. 1. Normal form. 

 2. var. acutilobum. One-half natural size. 



one from a plant of this kind. Since then many examples 

 of the class have been found, notably in Devonshire, and 

 they have been divided into aciitilohes, in which the 

 anterior and posterior rows of pinnules are of nearly the 

 same length, and divisilohes, which show a striking 

 further development of the posterior pinnules of each 

 pinna. The group furnishes many of the most remarkable, 

 constant and Vjeautiful of the myriad varieties of British 

 Ferns But it is not only in the Ferns whose fronds are 

 normally much subdivided that striking developnumt by 

 subdivision takes place. Look at the series shown in 

 Pig. 6 of subdivision in the Common Polypody. The 



type is seen to have )>iunu: (juite undivided. Then comes 

 var. gerratmn, which leads the way to var. semihcernm, and 

 we linally pass to the marvel- 

 lous var. corniihinnse, which 

 whi'ii fully develoj)ed is almost 

 ijuadripinnate. 



J. — MuKicATioN. — The last 

 grou]) includes those varieties 

 in which the surface of the 

 lamina has undergone altera- 

 tion. It isrlii<'fly ill the Hart's- 

 tougues that this character is 

 found. In numerous forms of 

 that species the surface is 

 broken by ridges and knobs 

 of leafy matter, variously dis- 

 posed. In var. giipralini'aftnn, 

 for instance, a narrow raised 

 line runs along the upper 

 surface on each side of the 

 midrib for the whole length 

 of the frond. In others the 

 edges are so lacerated that 

 upper and under surfaces 

 are almost indistinguishable, 

 and fructification frequently Common Polypody. 1. Norn 



form. 2. rar. serratum. 3. var. 



biense. One-half natural size. 



face of the frond. 



Lastly, a word as to 

 crossed varieties. Repeated experiments have shown that 

 the characters of one variety can be transferred to 

 another by sowing the spores of both varieties together, 

 which involves the inference that the antherozoids of 

 one prothallium may pass to a neighbouring pru- 

 tliallium and fertilize its archegonium. Botanists wn>re 

 very slow at first to admit the possiliility of this, 

 but the numerous crosses which now exist j^'o^'c 

 that it can and does occur. The means by which this 

 cross-fertilization has happened without artificial aid has 

 not been made clear. In some cases no doubt a continuous 

 water medium might exist between two prothallia, while 

 certain experiments of Mr. E. J. Lowe's* point to the 

 probability of carriage by small animals. A useful 

 artificial aid consists of a careful flooding of the prothallia 

 with tepid water when the sexual organs have arrived at 

 maturity. One of the earlier experiments of Mr. Lowe 

 was in itself conclusive. A robust normal form of Poly- 

 stichum aeuleaium (of which any cruciate variety was 

 unknown) was sown with a narrow cruciate variety 

 ( Wakeleyamun) of P. angulare. Five out of a thousand 

 seedlings obtained were cruciate P. aeuleatuin, of exactly 

 the type of Wakfleyanum.f This experiment, indeed, 

 also proves hybridization between the two species —but it 

 may be held that P. aeuleaium. and P. angulare are forms 

 of the same species. With this question we are not 

 concerned. The industry of Mr. Lowe, Col. Jones, Mr. 

 Carbonell, and many others, has now given us a multitude 

 of crossed varieties. By selected sowing, cresting has been 

 thrown into a large number of the most famous varieties, 

 such as A. F.-f. FrizdU;v and P. angulare dirisilohum. 

 Divisilobiim has been crossed with plumosum, giving a Fern 

 of marvellous beauty. Even variegation has been thrown 

 into various varieties, and other peculiar characters, such 

 a,s the fluxuose, congested, and ramose, have been similarly 

 combined by cross-breeding with well marked and constant 

 forms of other character. 



* Jonrn. Linn. Soc. (Botany), Vol. XXXII., p. 531, 189(5. 



t -SeeLowe,in^»»ai*o/Jote«^,Vol.III.,pp. 27-31, Plate 3, 18S9. 



