59S 



NA TURE 



[xAl'RIL 20, 1^9; 



and not clue to secondary elifects, owing to changes in the food 

 material, the following modifijations of the experiments were 

 carried out, and yielded most important and conclusive proofs 

 tliat the action nf ike rav< of lii]ht is direct on tin spores, and not 

 due to secondary actions owing to changes in the food materials. 



Two plates, for instance, of dried spores only are made, and 

 two of agar only, all as before. Then one plate of each kind is 

 exposed to the light, and the others are kept in the dark. 



After exposure, the stiff and moist film of non-exposed ■xz.'xx is 

 removed from its own plate, and superposed on the exposed film of 

 dried spores in situ. Reciprocally, the film of exposed agar is 

 removed, and superposed on the non-exposed film of dried spores. 



This prevents any wash or displacement, and ensures at the 

 same time thnt the agar shall present in contact with the spores 

 that face which was next the source of light. 



So far no apjireciable effect on the agar has been observed, 

 though the dried spores exposed for an equal period are killed 

 in abundance, as shown by the figure which comes out on 

 culture. 



Preliminary Results zuith the Spores of Fungi. 



Results substantially the same as the above are obtainable 

 with other Schizomycetes, but it was interesting to see whether 

 anything of kind occurs with the spores of true Fungi. The 

 time of year has, for many reasons, been unfavourable for 

 very numerous experiments, but the results so far are extremely 

 encouraging, and should give a stimulus to close inquiry into the 

 whole subject. 



The following species have been examined : — Penicillium 

 crustaceum, Aspergillus glaucus, Botrytis cinerea, Chalara 

 mycoderma, Oidinm lactis, Nectria cinnabarina, Mucor race- 

 mosHs, Saccharontyces pyriforinis, and a " Stysanus" conidial 

 form met with some months ago as a saprophyte on Pandanus. 



On making agar and gelatine plates of these as before, positive 

 re>uks were obtained with Oidinm {$ cases), Chalara (i case), 

 Saccharomyces (4 cases), Stysanus (2 cases), and negative results 

 with Aspergillus (5 cases), Penicillium (2 cases), Mucor (7. cases), 

 Nectria (4 cases), and Botrytis (2 cases). 



It seems worth noting that, in all the forms which have given 

 a positive result right off, the spores, as seen in masses, are 

 either hyaline and colourless, or, in the case of the Stysanus, 

 with a faint tinge of buff ; wliereas those which gave negative 

 results are either of some very pronounced colour, as Aspergillus, 

 Piniiilliuvi, a.nA N.ctria, or {Mucor and Botrytis) of a dull, 

 yellow-brown hue. 



After s;ime theoretical considerations, some practical bearings 

 of the results are thus referred to : — 



The establishment of the fact of the bactericidal and fungicidal 

 action of light, dating from Downes and Blunt to now, enables 

 us to see much more clearly into the causes of several pheno- 

 mena knoA'n to practical agriculturists, foresters, hygienists, &c. 



It helps to explain, for example, why the soil of a forest 

 should not be exposed to the sun, a dogma long taught in schools ; 

 it will also effect our way of regarding bare fallows. It has 

 already been shown how important is its bearing on the purifica- 

 tion of rivers, and the reasoning obviously applies to dwellings, 

 towns, &c. The author regards it as probably explaining many 

 discrepancies in the cultures of Schizomycetes and Fungi in our 

 laboratories, and as having a very important bearing indeed on 

 the spreading of plant epidemics in dull weather in the sum- 

 mer, and no doubt this applies to other cases. 



That sunshine has something to do with the rarity of bacterial 

 diseases in plants now seems quite as probable as the currently 

 accepted view that the acid nature of the latter accounts for the 

 fact. 



If that part of the chlorophyll which absorl)s the blue-violet 

 is a screen to prevent the destruction of easily oxidisable bodies, 

 as they are formed in the chloroplasts, we may reconcile several 

 old experimental discrepancies — e.g. the behaviour of plants 

 under bichromate and cupric oxide screens. 



The author concludes from his experiments, and from numer- 

 ous other considerations given in the paper, that the colours of 

 spores, pollen grains, &c., are of the nature of colour screens, 

 and is led to put forward the following hypothesis : — 



No plant expose: a reserve store of fatty food materials to the 

 danger of prolonged or intense insolations without a protective 

 colour-screen, calculated to cut out at least the blue violet rays, as 

 these rays would otherwise destroy the reserve substance by pro- 

 moting its rapid oxidation. 



MO 1225. VOL. 47] 



" Studies in the Morphology of Spore-producing Members. 

 Preliminary Statement on the Equiselacesc and Psiiotaceae." 

 II. By F. O. Bower, D.Sc, F.R.S., Regius Professor of 

 Botany in the University of Glasgow. 



Still maintaining the same general views as were put forward 

 in my preliminary statement on the Lycopodinae and 

 Ojihioglossacese (Roy. Soc. Proc, vol. 1. p. 265), I have now 

 investigated other types from among the Vascular Cryptogams 

 as regirds the development of their spore-producing members. 



Taking first the Equisetaceae, the development of the 

 sporangia has been closely followed by Goebel ; I find it, how- 

 ever, difficult to accept his conclusions as to the hypodermal 

 origin of the archesporium. On following the early phases of 

 development in Eq. arvense, the sporangium is found to be 

 eusporangia'e, but the essential parts of the sporangium may 

 be traced in origin to a single superficial cell, the cells adjoining 

 this laterally contributing only to form the lateral portions of 

 the wall. The first division of this cell is periclinal : the inner 

 resulting cell forms only a part of the sporogenous tissue ; the 

 outer cell undergoes further segmentation, first by anticlinal, 

 then by periclinal, walls, and the inner cells thus produced are 

 added to the sporogenous tissue, and take part in spore-formation. 

 The archesporium of Eq. arvense is thus shown to be not of 

 hypodermal origin in the strict sense ; the same appears to be 

 the case in Eq. limosum. Si liilar additions to the sporogenous 

 tissue by early periclinal division of superficial cells is commonly 

 to be seen in Isottes, and occasional cases, which are difficult to 

 explain in any other way, have been observed in some species of 

 I^ycopodium. It would thus appear that Goebel's generalisation, 

 that in all the V.ascular Cryptogams which he investigated a 

 hypodermal archesporium exists, cannot be retained in the strict 

 sen-e. The tapetum is derived from the series of cells immediately 

 surrounding the sporogenous mass ; it is, however, to be carefully 

 distinguished from certain cells of the sporogenous mass, which 

 also undergo an early disorganisation ; for about one-third of 

 the cells of the sporogenous mass do not form spores, but serve 

 physiologically as a diffused tapctum, yielding up their sub- 

 stance to nourish the other young developing spores. 



The synangia of the Psilotacese have given rise to voluminous 

 di-cussions. Tmesipterishtlag the genus with the simplerstruc- 

 ture, it may be described first. In their earliest stages of develop- 

 ment, as lateral outgrowths from the axi--, the sporangiophores 

 are not readily distinguishable from the foliage leaves in form 

 or structure, while they occupy a similar position upon the axis. 

 The first appearanceof asynangium is as an upgrowth of super- 

 ficial cells of the adaxial face of the sporangiophore, imme- 

 diately below its apex ; meanwhile the cells of the abaxial side 

 also grow strongly, while the apex itself does not grow so 

 rapidly ; so that the organic apex is soon sunk in a groove 

 between these stronger growths. The superficial cells which 

 are to form the synangium undergo periclinal and anticlinal 

 divisions, to form about four layers of cells. All the cells of 

 this tissue are at first very similar to one another, but later two 

 sporogenous masses become differentiated ; they are not, how- 

 ever, clearly defined while young from the sterile issue which 

 forms the partition of the synangium, or from the wall. From 

 the arrangement of the cells of these sporogenous masses it 

 seems not improbable that eaoh mass may be referable in origin 

 to a single cell, but this has not been proved to be constantly 

 the case. All the cells of the spoogenous tissue d > not arrive 

 at maturity, but here, as in Equiselum, a considerable number, 

 serving as a diffused tapetum, become disorganised without 

 forming spores. There is no clearly-defined tapetum in 7 inesip- 

 teris. The leaf lobes begin to be formed almost simultaneously 

 with the synaiigium, and appear as lateral growths immediately 

 below the apex of the sporangiophore ; their further develop- 

 ment presents no characters of special note. • 



The synangium of Psilotum originates in essentially a similar 

 manner, being formed from the upper surface of the sporan- 

 giophore, immediately below its apex. 



On the ground of the observations of internal development, 

 of which the above are the essential features, I agree with the 

 conclusion of Solms that the whole sporangiophore of_ the 

 Psilotacere is of foliar nature, and that the synangium is a 

 growth from its upper surface. 



In Lepidodendron the sporangium is very large ; it is narrow and 

 elongated in a radial direction, extending a considerable distance 

 along the upper surface of the leaf. I have already communi- 

 cated to the Society the fact thattrabeculse extend in Lepidoden- 

 dron from the base of the sporangium far up into the mass of 



