November i6, 1899] 



NA TURE 



67 



' OsmundaceK 

 Simplices Schizjeacect 



Gleicheniacec^ 

 Matonineae 

 I Loxsomacese 

 ! Hymenophyllacese 

 Gradatae { Cyatheaceoe 

 Dicksonieae 

 Dennstecliinece 

 /The bulk of the 

 \ Polypodiacese 



Mixtse .. 



Eusporangiatae. 



Leptosporangiatae. 



Mr. L. A. Boodle (Jodrell Laboratory, Royal Gardens, Kew) 

 gave an account, illustrated by numerous microphotographs, of 

 his researches into the stem-structure in Schizaeacea^, Gleich- 

 eniaceae, and Hymenophyllaceae. 



There is a wide difference between the types of stem-structure 

 shown by the different members of the Schizaeaceae. Lygodiuin 

 has a stele in which the xylem forms a central solid mass and is 

 surrounded by a continuous ring of phloem, pericycle and endo- 

 dermis. Anetmia Phyllitidis has a ring of separate bundles 

 (or steles) ; Mohria resembles Anetmia Phyllitidis in type. 

 Certain species of Aneimia, e.g. A. mexicana, have in the inter- 

 nodes a complete ring of xylem bounded on the inner and outer 

 side by a ring of phloem, pericycle and endodermis, with ? 

 central pith. Schizaea has a ring of xylem surrounding a central 

 pith, but no internal phloem or endodermis. 



The above four genera, which make up the Schizaeaceae, agree 

 in having a stem protoxylem, which is not well marked. 

 Lygodiuin, Aneiinia, and Mohria are exarch ; in Schizaea, 

 however, the relative position of the protoxylem has not been 

 made out with certainty. 



The Aneiinia iy^Q (which corresponds with that of a mature 

 Poly podium) may be regarded as the more specialised type 

 among the Schizaeaceae, and Lygodiuin (which corresponds in 

 structure with the base of the stem of Polypodium) as the more 

 primitive type. 



The Gleicheniaceae and Hymenophyllaceae also include forms 

 with a solid central mass of xylem, but differing in some details 

 from Lygodiiim. Gleichenia is mesarch and closely resembles 

 the fossil genus Heterangium. In the Gleicheniaceae the only 

 advance on the Lygodiuin type is found in Platyzoina, in which 

 there is a ring of xylem surrounding a central pith, as in 

 Schizaea, but differing from the latter plant in having an inner 

 endodermis. 



In the larger species of Trichomanes there is a solid xylem- 

 rnass, but with a group of parenchyma in connection with the 

 one or two more or less centrally placed protoxylems. In 

 Hymenophyllum the corresponding parenchymatous mass is 

 large in proportion to the amount of xylem. In the smallest 

 species of Trichomanes the stele of the rhizome takes the form 

 of a collateral bundle. The protoxylem of Trichomanes 

 spicatum, unlike the other species examined, resembles that of 

 the Schizaeaceae. 



The solid stele may be regarded as primitive, the Aneimia 

 type being derived from it by the following steps : — 



(i) Solid central xylem-mass surrounded by phloem, &c. 



(2) Ring of xylem surrounding a central pith. 



(3) Ring of xylem with internal phloem, endodermis, and 

 pith. 



(4) Ring of separate bundles formed by the breaking up of 

 the above vascular ring, owing to large leaf-gaps. 



Physiology. 



Sir William Thiselton-Dyer described some experiments of 

 far-reaching importance, made by Prof. Dewar, on the influence 

 of the temperature of liquid hydrogen on the germi native power 

 of seeds. The most important was one in which five kinds of 

 seeds, varying in size and composition, were immersed for six 

 hours in liquid hydrogen. The temperature to which they 

 were cooled was -453° F., below melting ice. They were 

 subsequently sown at Kew, and germinated readily without 

 exception (vide Proc. Koy. Soc, vol. Ixv. p. 361, 1899). 



The bearing of the experiment on the accepted conception of 

 protoplasm gave rise to some discussion. Protoplasm is con- 

 ceived to consist of physiological molecules, the properties of 

 which cannot be explained with our present knowledge of 

 either physics or chemistry. They are in a state of constant 

 kinetic energy based upon equally continual metabolic change. 



NO. 1568, VOL. 61] 



But if it is admitted that the latter is impossible at very low 

 temperatures, the former must cease and the evidence of life 

 disappears. The physiological molecule becomes purely static ; 

 its energy is wholly potential, and in fact it becomes, as 

 Prof. Casimir De Candolle has pointed out, analogous to an 

 explosive. 



Mr. Francis Darwin described some exceedingly interesting 

 investigations on the localisation of the irritability in geotropic 

 organs. The seedlings of Setaria, Sorghum and some other 

 grasses are remarkable for possessing a hypotcotyl or stalk-like 

 part intercalated between the grain and the cotyledon. Rolhert 

 has shown that while the hypocotyl is the motor apparatus, the 

 sensitiveness to light resides in the cotyledon, which transmits 

 a stimulus to the hypocotyl, and this results in curvature. The 

 author showed that the cotyledon is also a sense-organ for gravi- 

 tation, the stimulus which leads to geotropic curvature being iii 

 like manner transmitted to the hypocotyl. If a seedling of 

 Sorghum or Setaria is fixed by its grain to a support so that 

 the hypocotyl is horizontal, it bends upwards apogeotropically 

 till the cotyledon is vertical ; it then ceases to be geotropically 

 stimulated, and no longer transmits an influence to the region 

 of curvature. But if the conditions are reversed, if the seed- 

 ling is supported by its cotyledon (which is fixed in a horizontal 

 position) while the hypocotyl projects freely, the result is other- 

 wise. The hypocotyl begins to curve upwards just as in the 

 first experiment, but it does not cease to curve when the free 

 end points vertically upwards ; the curvature continues in- 

 definitely, so that the hypocotyl curls into a spiral of three or 

 four rings. This can only be explained by the assumption that 

 the geotropic sensitiveness resides in the cotyledon, and that 

 since the cotyledon remains horizontal it continues lo be stimu- 

 lated and transmits a continuous influence to the motor part 

 of the seedling. 



On Saturday morning some of the members of the Botanical 

 Section took part in a joint discussion with the Chemical Sec- 

 tion on symbiosis. Prof. Marshall Ward introduced the sub.- 

 ject by an able account of the meaning and significance Oi 

 symbiosis, as illustrated by numerous instances of symbiosis and 

 symbiotic fermentations afforded by various vegetable organisms*. 

 After describing particular cases of symbiosis, more particularly 

 of symbiotic fermentations. Prof. Ward dealt with the physiology 

 of symbiosis. 



Mr. J. Parkin (Cambridge) communicated some isolated ob,- 

 servations bearing on the function of latex. 



The author has lately returned from a year's sojourn in Ceylon, 

 where he has been acting as scientific assistant to Mr. Willis, 

 the Director of the Royal Botanic Gardens. During his time 

 there he has been principally engaged in investigations on 

 caoutchouc-yielding trees, chiefly Hevea brasiliensis (Para 

 Rubber) and Castilloa elastica, var. (a Central American rubber- 

 tree). The results of this research are contained in a recently- 

 published circular of the Royal Botanic Gardens, Ceylon, 

 entitled " Caoutchouc or India-rubber," intended primarily for 

 those interested in rubber cultivation. 



The author drew attention to some of the observations and 

 experiments recorded in the circular, which, besides their 

 practical value, have a general botanical interest ; he also 

 recorded other observations which may throw light on the 

 functions of laticiferous tissue. 



The points treated of in the paper were grouped under six 

 sections : — 



Section I. dealt with the coagulation of the latex of Hevea. 



Section II. contained observations and remarks relating to 

 the carbohydrates of latex. 



In Section III. reasons were given for thinking that in some 

 caoutchouc trees the latex of the young stems and leaves difters 

 in composition from that of the trunk and main branches. 

 While the latter yield rubber free of stickiness, the former give 

 a somewhat viscous substance with feeble elasticity. Such is 

 the case with Hevea, Castilloa, Landolphia,Kirkii, &c. 



Section IV. treats of an important fact connected with the 

 tapping of Hevea trees— namely, that wounding the bark causes 

 a greater flow of latex from subsequent injuiies. 



In Section V. a peculiarity in the e^iud^tion of latex frpm the 

 severed base of the petiole of Hevea brasiliensis and Plumiera 

 acutifolia was described and discussed. 



And in Section VI. a special laticiferous system in the im- 

 mature seed of Hevea brasiliensis was described. 



The paper concluded with general remarks and suggestions on 

 the origin and functions of laticiferous tissue. 



