364 



KNOWLEDGE. 



September. 1910. 



been cut from the host-plant. To obtain quite ripe spores, 

 which will germinate readily, it is necessary to gather them on 

 a warm. dry. still day. This memoir is of importance since it 

 opens up a wide field for further work on the ecology of fungi : 

 our knowledge of the dispersal and .germination of fungus 

 spores in nature is very scanty, even as to fungi of ecomonic 

 importance. 



THE "Sl'IKi;" OF THK OPHIOCiLOSSACKAK.— 

 There has been nmch discussion concerning the nature of the 

 spike, or sporangiophore, or fertile leaf-segment, of the 

 .Adder's- tongue (O/i/z/o^/oss/hh). the Moonwort {Hutrycliiiiiii), 

 and their allies, together forming the group Ophioglossales. 

 which is now reg.arded as standing quite apart from the true 

 ferns iFilicalcs). The question has now been attacked from 

 the standpoint of vascular anatomy by Chrysler 1.4;;;!. Bot.. 

 1910), who has obtained some important results. The " fer- 

 tile spike " is regarded as representing two fused leaflets — the 

 lowest pair — of a pinnate fern leaf. It must be admitted that 

 this is clearly indicated only in certain species of Botrycli in in . 

 but it is difficult to see how the facts brought forward In- 

 Chrvsler can be interpreted otherwise than as almost con- 

 clusive evidence that the '" spike " represents two fused pinnae, 

 or (in Hclininthostachys) a single pinna, and that the 

 "sporangiophore" theory has been disposed of. Chrysler 

 suggests that the ()phio,glossaceae have sprung from near the 

 level of the Osnnmdaceae among the lower ferns. 



THE LIFI' HISTORY OF LAMI \ AKI.A.— A most 

 interesting paper has been pviblished by Drew (.4;n(. Bot., 

 1910),a worker at the Plymouth Marine Biological Laboratory, 

 from which it appears that the reproductive organs of the 

 common Sea Tangle (Lainiiiaria) are not merely sporangia, 

 producing zoospores which give rise directly to new plants, 

 but are gamctanjiia, producing gametes or se.xual cells which 

 conjugate in pairs to form zygospores. The zygospore gives 

 rise to a chain or mass of cells, and from this the young 

 Lainiiiaria plant grows out directly. The gametes when set 

 free into the water apparently have no cilia, but soon develop 

 these. Drew considers that Lainiiiaria shows an alternation 

 of generations, the plant itself being the .v generation, while the 

 " chain or mass of cells " arising from the zygospore represents 

 the 2.V generation. This inference is, however, rather doubt- 

 ful ; no cytological evidence is given, and the direct outgrowth 

 of the young Lainiiiaria plant from the supposed 2.x- genera- 

 tion is not suggestive of an inter\ening reduction di\ision. It 

 is greatly to be hoped that the cytology of Lainiiiaria will 

 shortly be worked out in detail. 



APOSPORY IN MOSSES.— Some time ago. El. and Em. 

 Marchal showed that when a leafy Moss-plant is induced to 

 grow from a fragment of the stalk of a Moss capsule — that is, 

 when apospory occurs and the sexual generation arises directly 

 from the asexual without the intervention of the spore itself — 

 the Moss-plant thus obtained is always hermaphrodite, or 

 monoecious, even in species which are normally dioecious, 

 e.g. Mniitin horiiicin. These authors have followed up their 

 earUer work, and in a recent paper {Bull. Ac. roy. Belg., 19091. 

 they report that these hermaphrodite plants, arising from 

 apospory in dioecious Mosses, are sterile. They also record 

 the following very remarkable observations. Ill The plants 

 arising from apospory in monoecious Mosses show normal 

 sexual characurs, and are fertile, producing 4.v sporophytes 

 and 2.x spores, and thus giving rise to a permanent race with 

 Vuvalent nuclei. (2) The regeneration of the 4.v sporophytes 

 gives rise, in turn, to 4.v gametophytes ! This a,stonishing 

 result follows from the apparent absence of any supplementary 

 reduction or any process of apogamy, by which the doubling 

 of the chromosomes can be avoided. (3) The comparison of 

 homologous organs in the x, 2x. and 4.v gametophytes and in 

 the 2x and 4.v sporophytes shows the existence of a direct 

 relation between chromosome-number on one hand and the 

 size of nucleus and cell on the other. This increase in size 

 of the cells results in augmented size of the sexual organs 

 themselves. (41 The aposporous origin of the Moss-fruit 

 actu.ally occurs in iiatiuc in \arious species of Mosses, as a 



result of wounds and other injurious influences, the bivalent 

 races thus produced being readily distinguished from the 

 corresponding normal types by the increased sizes of the 

 sexual organs. 



RECENT RESEARCHES ON TRANSPIRATION.— 

 The great importance of transpiration — the gi\ing-off of water 

 vapour by the aerial green organs, especially the foliage- 

 leaves, of plants — has led to a vast amount of research in 

 recent years, doubtless because of the increased attention 

 that is being paid to ecology, and because water forms the 

 most important factor in the environment of plants. 



(1) Thoday and Sykes {.Ann. Bot.. 1909) describe some 

 experiments on what they term " the transpiration current in 

 submerged water-plants." That movement of water occurs 

 in the stems of submerged aquatics has long been known, but, 

 though these new observations certainly give clear evidence of 

 such movement, it is surely misleading and erroneous to apply 

 the term " transpiration current " in the case of these plants, 

 in which there cannot be any question of a true transpiration 

 process. 



(2) Bergen (Bot. Gaz.. 1909) in an interesting paper on " the 

 modifiability of transpiration in young seedlings." concludes 

 from his experiments that plants grown in a highly humid 

 atmosphere acquire a much greater than normal capacity for 

 transpiration in a moderately dry atmosphere ; that different 

 genera of the same family vary greatly in their capacity to 

 acquire by such culture a tendency to extremely rapid 

 transpiration ; that the transpiration rate becomes notably 

 greater as the leaf becomes fully developed ; and that 

 transpiration is not necessarily greater when the relative 

 humiditv of the air is very low than when it has a medium 

 value. 



(3) Sampson and Allen [Minnesota Bot. Studies, 1909) 

 set out to determine the influence of physical factors on 

 transpiration. They find that plants developed in sunlight 

 lose from iwo to four times as much water as plants of the 

 same species developed in shade ; that increase in altitude 

 produces increased transpiration, the effect being due solely 

 to the diminished barometric pressure ; that transpiration is 

 directly related to internal structure in amphibious as compared 

 with land plants, the chief factor being the presence in the 

 former of abundant air-chambers in the stem ; that acid 

 solutions accelerate and alkaline solutions retard transpiration, 

 and weak solutions often produce as marked effects as strong 

 ones. 



(4) Puglisi {.Aiinalt di Bot.. 1909) devotes a long and 

 detailed paper to the transpiration of Dicotyledonous ever- 

 greens in winter, spring and summer. He investigated the 

 rate of the transpiration current in detached shoots by means 

 of the potometer — his results showing certain discrepancies 

 due to unwary use of this apparatus, by the way ; and he also 

 compared, by means of Garreau's well-known method, the 

 transpiration from the upper and lower sides of the leaves 

 experimented with. Puglisi's chief conclusions are : that the 

 volatile oils present in evergreens are highly efficient in 

 preventing excessive transpiration ; that the safeguards against 

 injurious transpiration do not prevent rapid transpiration 

 when there is an adequate water supply from the roots ; that 

 the relative transpiration rate of the upper and lower leaf 

 surfaces varies decidedly at different seasons ; and that for 

 evergreens transpiration shows a minimum in winter, a maxi- 

 nuun at the beginning of spring, and a lowering to, or nearly 

 to, the winter rate during the heat and drought of summer. 



(5) Reed iBot. Gaz., Feb., 1910) has made a careful 

 study of the effects of certain chemical agents, chiefly 

 salts, upon the transpiration of wheat seedlings, in relation 

 to the effect of the same compounds upon the growth 

 of the plants. He finds that transpiration is increased 

 by lime, by sodium phosphate, and by tannic acid ; it is 

 diminished by potassium salts, and usually by sodium nitrate ; 

 while the effects of organic acids are variable. These effects 

 appear in all cases to be a specific action of the ions constitut- 

 ing any given agent. For instance, potassium always inhibits, 

 while calcium always accelerates transpiration, whether 

 combined to form chloride, nitrate, or sulphate. Reed notes 



