October, 1912. 



KNOWLEDGE. 



391 



of Lycopods was derived from the same ancestry. The 

 revolt against this view was led by Campbell himself, and the 

 opposite position is now accepted. 1 n his great series of memoirs 

 on the I'toridophyta in the Pliilosopliicul Transactions, Bower 

 showed that the terms "eusporangiate" and "leptosporangiate" 

 must be abandoned as the names of groups, though useful in a 

 purely descriptive sense. In Bower's classification, the small 

 family Ophioglossaceae is separated, as Ophioglossales, from 

 the remaining ferns which are classed as Filicales. The 

 Filicales are divided into three main groups of families accord- 

 ing to the characters of the sporaiigial clusters (sori) and of 

 the sporangia themselves, the three groups being termed 

 " Simphces," " Gradatae," and " Mi.xtae." In the Simplices 

 (including Marattiaceae, Osmundaceae, and others) the spor- 

 angia of a sorus arise simultaneously ; the mechanism for 

 dehiscence of the sporangium is slightly developed, and the 

 spore-output per sporangium is large. In the Gradatae 

 (Hymenophyllaceae, Cyatheaceae, and others) the sporangia 

 are produced on a more or less elongated rod like placenta, 

 and are developed on this in basipetal order (the oldest above, 

 the yoimgest below), while the dehiscence mechanism is well- 

 developed and the spore-output is smaller than in the 

 Simplices ; in the Mixtae, the sporangia of a sorus arise in no 

 definite order; hence the sorus contains sporangia of various 

 ages mingled together, the mechanisms for dehiscence and 

 usually also those for protection of the sporangia are more 

 perfect, and the nmiiber of spores per sporangium is usually 

 restricted to sixty-four or sometimes forty-eight. 



Campbell, however, points out in his memoir that the isola- 

 tion of the Ophioglossaceae, as Ophioglossales. on one hand, 

 and the inclusion of Marattiaceae with the remaining ferns in 

 the Filicales, on the other, hardly do justice to the close 

 affinities that exist between the Ophioglossaceae and the 

 Marattiaceae. The author's detailed and skilful presentation 

 of the facts of structure and development in these two families 

 make this one of the most important botanical memoirs 

 published in recent years. In the case of each family, he 

 describes and compares the structure and development of the 

 several genera, dealing in turn with the germination of the 

 spore, the prothallus and sexual organs, the embryo, and the 

 young and adult stages of the sporophyte, thus completing the 

 life history. 



The greater part of the volume is based upon the author's 

 own work, the material for which has chiefly been collected 

 by himself in various parts of the Tropics. In the case of 

 every form worked at, various gaps in former accounts have 

 been filled, the result being that we have here perhaps a more 

 complete picture than exists at present for any other group of 

 the higher plants. After a survey of the morphology of the 

 two families, the author brings out clearly the strength of the 

 links connecting these families. On various grounds he 

 concludes that of the three genera of Ophioglossaceae, 

 Opiiioglossiini is decidedly the most primitive, while Hel- 

 inintliostacliys on the whole comes nearest the Marattiaceae, 

 the simplest and presumably most primitive genera of the latter 

 family being Kaiilfussia and Danaea, while Marattia and 

 Antiiopteris are the most specialised. 



The author believes that from some form allied to the 

 simpler existing species of 0^/;/o^/oss!</« the whole fern series 

 has arisen ; that in this whole series the leaf is the predomin- 

 ant organ, the stem at first being of quite subordinate import- 

 ance : that this ancestral fern was one-leaved, the leaf being 

 at first a fertile (spore-bearing) structure, perhaps without any 

 definite sterile segment : and that from this central type several 

 lines diverged, of which only a few fragments persist. 



SCOTTISH PEAT DEPOSITS.— During the last seven 

 years F. J. Lewis has published the results of his elaborate 

 investigation of the plant-remains in the peat deposits of 

 Scotland, and in his concluding paper iTrans. Roy. Soc. 

 Edinburgh. XL\'ll) he gives a summary of the sequence of 

 the layers found in these deposits, as follows : — 



1. First Arctic Bed. probably corresponding to Geikie's 

 Fovirth Glacial Stage, with ice-sheets and valley glaciers, 

 arctic climate with snow-line from one thousand to one 

 thousand five hundred feet; in the Hebrides and Shetlands 



the beds contain dwarf willows, birch, crowberry, various 

 temperate water-plants, and so on. 



2. Lower Forcstian. Fourth Interglacial Stage, consisting 

 of forest overlying morainic accumulations of the Fourth 

 Glacial Stage, genial climate, land area of greater extent than 

 now ; the buried forests, seen in the southern uplands as well 

 as in the Hebrides and Shetlands, contain birch, hazel, and 

 alder — showing that the now treeless West Shetlands had a 

 calm and genial climate. 



3. Longer Peat Bog.with Sphagnum, coUon-sedge,Molinia, 

 and so on, and in the lower layers also Phraginites,Equisctuni, 

 Menyanthcs. 



4. Second Arctic Bed, widely distributed, with willows, 

 crowberry, Loiseleuria, Arctostaphylos alpina, birch. 

 Lychnis alpina, and so on. 



5. Upper Peat Bog, still more widely spread, and similar 

 to the lower bog in general characters. The Lower and Upper 

 bogs, with the intervening Second Arctic Bed, probably answer 

 to Geikie's Fifth Glacial or Lower Turbarian Stage of valley- 

 glaciers, with average snow-line at about two thou.sand five 

 hundred feet, and cold, wet climate. 



6. Upper Forestian, or Fifth Interglacial Stage; in the 

 south this upper forest consists chiefly of Scots pine, replaced 

 in the north and at high altitudes by birch, and extends to 

 over one thousand feet higher than the present limit of trees ; 

 the climate was relatively dry and genial. 



7. Recent Peat, Sixth Glacial or Upper Turbarian Stage, 

 with high level glaciers, snow-line at three-thousand five 

 hundred feet, climate rather cold and wet. 



LIFE HISTORY OF PV'A'O.Vfi.U.4.— A large amount of 

 cytological work has been done on the .\scomycetes since 

 Harper showed, in 1895, that in the mildew Sphaerotheca 

 castagnci two nuclear fusions occur in the life-cycle — the 

 first in the female cell or oogonium and the second in the 

 young ascus. In 1900 ^Ann. Bot.) Harper published a long 

 paper based largely on his work with the small ascomycetous 

 fungus Pyronema confluens, in which he claimed that the 

 nuclei of the antheridium and oogonium — the male and the 

 female nuclei — fuse in pairs, the fusion-nuclei passing into 

 the ascus-producing threads ; in the young ascus, as in 

 Sphaerotheca, a second nuclear fusion occurs, preceding the 

 division into the eight nuclei of the developing ascospores. A 

 voluminous and somewhat controversial literature has resulted 

 from the extension of this line of work to other fungi. 



Claussen has now iZeitschr. fiir Bot.. 19121 published an 

 elaborate paper, beautifully illustrated by six double plates, on 

 the Ufe history of Pyronema confluens, together with a 

 critical commentary on the results of other workers. He finds 

 that the male nuclei enter the oogonium and pair with the 

 female nuclei, though no fusion occurs between the paired 

 nuclei. These pass out into the ascogenous hyphae and there 

 undergo division, still remaining paired but not fused. 

 Finally, the descendants of these nuclei fuse in the young 

 ascus. In the young ascus there is a pair of nuclei, one male 

 and the other female, and these divide into a paired nucleus 

 for the ascus and two reserve nuclei ; the paired nuclei fuse, 

 giving one nucleus, and this divides with reduction of 

 chromosomes (heterotypic division!. Hence, in the life cycle 

 there is a single fusion and a single reduction division. The 

 sporophyte generation, represented by the ascogenous hyphae, 

 is therefore not sharply separated from the gematophyte 

 generation : its nuclei are paired, the double number of 

 chromosomes being present in the coupled nuclei and not in a 

 single nucleus. The young ascus represents the spore mother- 

 cell, its fusion-nucleus containing as many double chromosomes 

 as the gametophyte nuclei contain single ones. A similar 

 pairing of sexual nuclei, without fusion until a relatively late 

 stage in the life cycle, occurs in the Uredineae, as shown by 

 Blackman and others. 



PHYSIOLOGY OF TREES.— Some interesting results 

 have recently been obtained by Ramann and Bauer ijalirb. 

 fiir 'iCiss. Boi.. 1911 ) from investigations on a large scale of 

 the changes in dry-weight and ash-composition in the saplings 

 of a number of trees. In spring, during the expansion of the 



