350 



KNOWLEDGE. 



September, 1911. 



embryonic state, these areas being along the veins ; and that 

 the impulse to development, apart from external stimuli, is 

 conditioned by the presence of the necessary constituents of 

 the food, brought about in leaves — when the leaf-stalk is cut — 

 by the retention of the leaf's products within itself. 



The phenomena of regeneration in plants have been much 

 studied, and the results obtained by experimental researches, 

 in which the plant is injured or has various organs removed, 

 depend primarily for their interpretation on the fact that the 

 various parts are correlated and influence each other. That 

 is, we may assume that every organ arising from growing cells 

 may develop in a variety of ways, and the direction of develop- 

 ment which it takes depends upon its relations to other parts. 

 When a stem or root is amputated, as in making cuttings, the 

 new organ arising may be already present as a rudiment near 

 the wound, or it may be formed from the healing tissue 

 (callus). As a rule, leaves or parts of leaves cannot be 

 replaced, but this does happen in some plants : as, for instance, 

 in Cvclitiiieii pcrsicitin, where new leaf-blades arise on the 

 leaf-stalk when the blade of a young leaf has been cut off, 

 Goebel states that in this case there is no real renovation of 

 the leaf-blade, but simply a continued growth of the leaf-base, 

 which was previously inhibited owing to correlation. 



A remarkable feature in regeneration is the polarity of the 

 organs and of the individual cells. If the tip of a shoot is 

 removed, the bud nearest the wound develops : if the tip of a 

 root is cut oft", the nearest lateral root takes its place. A cut 

 willow branch, bearing buds, will, if kept in moist air, produce 

 at its upper end shoots only, and at its lower end roots only, 

 whether it is placed right way up or inverted. The branch 

 has an inherent polarity of its own, which was for long 

 regarded as fixed ; but Klebs showed that if the cork is 

 removed from the upper end of a cut willow branch, and this 

 end placed in water, roots will then develop from this end — by 

 allowing enough water to enter, owing to the removal of the 

 cork, the internal polarity of the branch is upset. 



Doposcheg-Uhlar {Flora, 19111 has investigated the 

 regeneration and polarity in various plants, and has obtained 

 some remarkable results. He finds that the new shoots which 

 arise from a very young fern-plant, still attached to the pro- 

 thallus. when the growing-point of the plant is removed, strongly 

 resemble the young fern produced from the fertilised egg ; 

 there arises first a " cotyledon " independent of the growing- 

 point of the shoot. In some cases, moreover, the shoots 

 arising from cut pieces of fern rhizome (underground stem) 

 showed a curious leaf-like structure which protected the 

 young growing-point, in much the same way as the cotyledon 

 of the young fern plant protects the stem apex in its early 

 stages of growth. 



Many other interesting experiments are described by 

 Doposcheg-Uhlar, whose paper is a model of patient and 

 ingenious work directed towards the establishment of new- 

 facts, and the solution of the many problems arising from the 

 stimulus given by Goebel in his invaluable Einlcitung. 



It is much to be hoped that Goebel's book will be translated 

 into English. The earlier work on experimental morphology, 

 regeneration, polarity, and allied topics is well summarised in 

 Jost's " Plant Physiology " (Oxford Press), 



SPORE DISPERSAL IX SELAGINELLA, — Various 

 recent contributions to our knowledge of the genus SclagiiwHa 

 have been noted in these columns. This time we have 

 to note an interesting paper by a German worker, F. W. 

 Neger, who has descrilsed the shedding of the spores in 

 Sclaginella helvetica and S, spiniilosa, in a recent number 

 oi Flora (N.F., Band 3. 1911). 



In 1901, Goebel {Flora, Hand S8) showed that in various 

 species of Sclaginella examined by him the megaspores are 

 shed spontaneously, owing to a curious mechanism in the 

 structure of the sporangium wall. The structure of the 

 microsporangium is much simpler, the dehiscence mechanism 

 being less highly developed, so that the microspores, despite 

 their much smaller size, are scattered less widely than the 



large megaspores. He also showed that the cones or 

 " flowers " of Sclaginella are usually protogynous, that is, 

 the megaspores are shed before the microspores, though the 

 latter germinate much more rapidly. These arrangements 

 tend to prevent self-fertilisation, or the fertilisation of the 

 eggs, produced on germination of the megaspores, by the 

 male gametes produced on germination of the microspores of 

 the same plant, 



Neger has investigated the dorsiventral creeping species 

 S, heli'cfica, and the radially symmetrical erect species 

 i>', spinnlosa. On each cone there occur at the apex 

 microsporangia, at the middle both kinds of sporangia, and 

 at the base microsporangia again. The apical microsporangia 

 open first, then the two kinds of sporangia in the middle 

 region, and finally the basal microsporangia. That is. in 

 these two species the cones are at first protandrous, but after 

 the emptying of the whole of the megasporangia there are 

 always present undehisced microsporangia ; there are two 

 crops of microspores, some shed before the megaspores, and 

 the rest afterwards. Hence during the whole of the period 

 of shedding of megaspores there are ripe microspores ready 

 to germinate. 



In S. helvetica, Neger finds that the cones as well as the 

 creeping vegetative shoots show dorsiventral symmetry, the 

 upper leaves being small and the lower ones large. This 

 species grows chiefly on vertical rock faces. In the middle 

 region of the cone, which grows upwards from the creeping 

 shoot, the megasporangia are chiefly found on the ventral side, 

 the microsporangia chiefly on the dorsal side. This arrange- 

 ment, which does not appear to have been previously noted, 

 is attributed by Neger to the better nourishment of the ventral 

 side owing to the larger leaves. Moreover, the ventral side is 

 turned towards the light, and its leaves are. therefore, in a more 

 favourable position for assimilation. Much more food is, of 

 course, required by the megaspores, the tissue of which has to 

 nourish the developing embryo, than by the minute microspores 

 which merely have to produce a few antherozoids. Since S, 

 helvetica grows in sheltered clefts and crannies, wind can only 

 play a small part in the dispersal of the spores. The dehiscence 

 mechanism of the niegasporangium is well developed, but this 

 mechanism would be of little use were the megasporangia on 

 the shaded dorsal side of the cone — the liberated megaspores 

 would then strike the vertical rock face close to the plant and 

 roll oft' or become entangled in the vegetative shoots. The 

 minute microspores, however, are easily carried away by the 

 lightest breeze, and the dehiscence mechanism in the micro- 

 sporangium wall is so feeble that the spores on being set free 

 hardly reach the substratum close by. In S. spinnlosa, 

 which forms horizontal patches with the shoots orthotropous 

 (erect), the cone shows no difterentiation into light and shade 

 sides ; the megasporangia are found all round the axis of the 

 cone, and the megaspores on being set free have a clear path 

 in all directions. 



CHEMISTRY. 



By C. .\iNS\voKTH Mitchell. B.A. (Oxox,), F,I.C, 



BIOLOGICAL ACTION OF RADIUM.— Dr. Loewenthal 

 writing in ihe Zeif. aiigeicandf. Chein.. 1911, XXIV, 1130, 

 points out that the therapeutic action of certain mineral water 

 springs must be attributed, partially at all events, to their con- 

 taining a considerable proportion of radium. It is well known 

 that radium emanation has a pronounced stimulative effect 

 upon the enzymes (pepsin, trypsin, diastase) present in the 

 body, and the beneficial eftects of these springs are probably 

 due to this cause. Young plants and mould-fungi are also 

 favourably influenced by the action of a small quantity of 

 radium emanation, but they are injured by larger amounts. 

 The action of the i-adium emanation has also a marked effect 

 upon the white corpuscles of the blood, and it has been 

 proved by Gudzent that the same body increases the solubility 

 of sodium urate. This effect, however, is attributed to the 

 action of the product of decomposition of the emanation 

 termed " radium D." On this fact has been based a method 



