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SCIENCE- G OSS IP. 



the formation of tissues. The protoplasm appears 

 to possess in each cell or set of cells the capacity 

 of forming cell-walls in certain fixed planes. In 

 fact, it is said to be influenced by a directive 

 action, these planes being tangential, radial, or 

 transverse, if we are considering an elongated 

 structure like a stem or root ; or merely parallel to, 

 or at right angles to the surface, if we are dealing 

 with a thalloid one. Moreover, there is a certain 

 amount of symmetry to be observed in individual 

 tissues, in the arrangement of the cells relative to 

 one another. If we take for consideration the pith 

 of any succulent stem and examine transverse 

 sections, first of all through the bud and then 

 through the older portions of the stem, we shall 

 find the following points to hold good : — In the 

 bud the young pith cells are crowded together, 

 but retain more or less of their original ovoid 

 shape, and the intercellular spaces are large. There 

 is little regularity to be seen in the transverse 

 section, but a longitudinal one shows us that the 

 young medullary cells are laid down by the sym- 

 metrical formation of fresh "periclinal" and 

 " anticlinal " cell-walls. In the older pith a great 

 many subsequent divisions have arisen, and the 

 cells are so crowded together that they are no 

 longer oval in contour but polygonal. A point to be 

 observed is the fact that in a transverse section the 

 majority of these cells, as also those of the cortex, 

 are hexagonal. In fact, wherever cells are massed 

 together like this, the resultants of turgidity and 

 cohesion tend to produce, first of all, the hexagonal 

 shape, and, later may be, a polygon of any number 

 of sides (fig. 2). Of course there may be inter- 

 mediate forms, such as 5-sided, or even square cells. 

 The majority are, however, hexagons, as I have 

 repeatedly verified by counting. This fact calls to 

 mind the experiments of Plateau with thin films, 

 in which surface-tension takes the part which the 

 pressure caused by turgidity does here ; small 

 soap-bubbles held together by surface-tension 

 enclose spaces, analogous to our cells, that are 

 some multiple of hexagon. Turgid cells thus obey 

 the law of thin films, which states that the surface- 

 tension acts in such a way as to cause these films 

 to present the least area compatible with stability. 

 It is in this manner that we get hexagonal sym- 

 metry in crowded tissues. Thus we have symmetry 

 produced in two ways ; first, there is that conse- 

 quent on the regular formation of cell-walls parallel 

 or perpendicular to certain fixed surfaces. Then 

 there is the symmetry arising'from purely physical 

 causes, such as cohesion, turgidity, and in some 

 cases surface-tens-ion. The first of these may be 

 teimed inherent ; the second, which only applies 

 to young or veTy thin-walled tissues, physical. 

 The first brings about symmetrical arrangement of 

 tissues ; the second, symmetry in the grouping 

 together of cells. 



Kecent Kesearch. — Kornicke (Ges. Nat. u. 

 Heilkunde, Bonn) describes the peculiar process of 

 the passage of nuclei through cell-walls. In Crocus 

 this is effected by means of the strands of proto- 

 plasm that connect neighbouring protoplasts with 

 one another. All the cells in a pollen-chamber 

 would sometimes exhibit partial passage of nuclei. 

 Professor D. H. Campbell, continuing his former 

 researches on Peperomia, has determined that all 

 species of the genus seem to have sixteen nuclei 

 in the embryo-sac instead of the normal eight. 

 Usually eight nuclei fuse to form the definitive 

 nucleus, and they are the homologues of the polar 



nuclei of typical angiosperms. In Peperomia we 

 have, according to Professor Campbell, the most 

 primitive type of Angiosperm. Dr. A. Jencic gives 

 a curious result in connection with the germination 

 of seeds at low temperatures. He finds that in air- 

 dried seeds exposure to —18° Cent, accelerates the 

 power of germination, due possibly to the trans- 

 formation of insoluble carbohydrates into those 

 soluble in water. A. Burgerstein (Oesterr. Bot. 

 Zeitschrift) communicates some of the results 

 obtained by Professor Anton v. Kerner on the 

 opening and closing of flowers. In many cases it 

 appears that the phenomena in question are not 

 the result of growth, but are caused by changes in 

 turgor, due to transpiration. A new chromogen 

 producing a red pigment has been found in 

 Sehenckia blumenaviana (Eubiaceae). The pigment 

 is stated (" Journal of Microscopy," October 1901) 

 to be the probable result of the action upon its 

 chromogen of an enzyme, and is not identical with 

 rubian or phycorythrin. 



Specific Irritability.— The fact that proto- 

 plasm in one part of a plant is capable of pro- 

 ducing cells having an entirely different form and 

 function from those in another part of the same 

 organism has for some time been attributed to the 

 fact that there is some intrinsic difference in the 

 response to stimuli in these two parts. In other 

 words, it is to the property possessed by the proto- 

 plasm of different cells, knowm as "specific irri- 

 tability." In the young tissue of a bud where, 

 before this property has begun to exert an influence, 

 the cells are histologically alike in every respect, 

 we find very soon that different systems of tissues 

 begin to arise, and that, without any obvious 

 external influence. There are, of course, stimuli at 

 work in the shape of nutrition and the maintenance 

 of an optimum temperature and degree of moisture, 

 but there is something else which has to be 

 assumed, and that may be looked upon as inherent 

 in protoplasm, either transmitted with the proto- 

 plasm of seeds of former generations, or partly this, 

 and partly the effect of various physical forces. 

 "Specific irritability " is well demonstrated in the 

 effect of various chemical agents upon different 

 plants. To some, iodide of sodium, for example, in 

 dilute solution acts as a food material ; to others it 

 is directly harmful, and yet others are not affected 

 at all. This chemotaxy is only another manifesta- 

 tion of specific irritability. The intrinsic property 

 we are here considering is brought into play 

 very strongly during the reproductive processes, 

 especially in the fertilisation of the egg-cell 

 by the generative nuclei of the microspore. 

 In . this case we have a species of chemotaxy, 

 and it has been shown in the case of VauoTieria 

 sessilis that the oospore secretes a plug of mucilage 

 which contains malic acid that .exerts a posi- 

 tive chemotaxis upon the antherozooids. Here, 

 of course, we have a manifestation of irritability 

 probably peculiar to both bodies, and which results 

 in the fusion of these to form the oospore. After 

 all has been said, however, we can only be certain 

 of one thing, and that is, that this irritability, 

 which is manifested in such a variety of ways, is 

 intimately dependent upon the vitality of proto- 

 plasm, by which is meant the elementary property 

 of protoplasm to react to stimuli. What it is that 

 causes this reaction to vary in different cells is a 

 matter which is yet under discussion. The con- 

 sideration of chemotaxy is, therefore, useful in 

 throwing light on the subject. 



