June 4, 1909] 



SCIENCE 



905 



tion," while the " Zx-generation " comprises the 

 sporogenous cells of the cystocarp and the entire 

 tetrasporic plant. It seems hardly likely, how- 

 ever, that the tetrasporic plants are analogous, 

 save in the number of chromosomes, to the sporo- 

 phyte of the archegoniates. 



Vegetative Reproduction iy Induced Root-regen- 

 eration in the Guayule: Feancis E. Lloyd, 

 Alabama Polytechnic Institute, Auburn, Ala. 

 Parthenium argentatum (the Mexican guayule) 

 and P. incanum (the Mexican mariola) are two 

 woody perennials belonging to the Compositse and 

 are found in the northern part of the central 

 plateau of Mexico. A comparison of these two 

 species discloses certain differences in the methods 

 of vegetative reproduction which have already 

 been described by the writer. These differences 

 appear to be quite constant in nature. It is, 

 however, possible by experimental methods to 

 force the guayule (Parthenium argentatum) to 

 adopt the method of vegetative reproduction which 

 is normally followed by the mariola {Parthenium 

 incanum). The paper, of which this is an ab- 

 stract, describes the experimental conditions and 

 the results obtained. 



The Morphology of the Peridial Cells in the 

 Roestelice: Fbank D. Keen, Purdue University, 

 Lafayette, Ind. 



The value of the sculpturing on the peridial 

 cells as a specific character in defining the species 

 of Roestelia has already been ably pointed out by 

 Dr. Ed. Fischer and a number of the American 

 forms have been figured and described by him. 

 Aside from the surface markings there are a num- 

 ber of other features about the peridial cells which 

 are worthy of consideration. It is for the purpose 

 of setting forth the microscopical structure with 

 some detail that this paper is presented. The 

 part played by the peridial cell in making the 

 different appearance between the forms of Roe- 

 stelia and ^oidium is discussed. The chief atten- 

 tion, however, is given to the various types of cells 

 and to an explanation of the terms used in de- 

 scribing them. Concrete examples, including many 

 little-known species in addition to the more com- 

 mon ones, are given, together with a number of 

 illustrations. 



The Effect of Certain Salts upon Transpiration 



and Growth in Wheat: Howabd Speagtie Reed, 



Virginia Polytechnic Institute, Blacksburg, Va. 



An investigation has been made of the effect of 



some chemical compounds upon the amount of 



transpiration per unit of growth in wheat plants. 



The results are expressed in terms of the units of 



water transpired per unit of increase in plant 

 substance and by curves which show graphically 

 the increments in transpiration and growth in 

 comparison with control cultures. The data were 

 obtained from several thousand wheat cultures 

 grown in a variety of soils in paraffined wire pots, 

 or in water cultures. Salts of sodium and potas- 

 sium decrease the amount of water transpired per 

 unit of growth, while salts of calcium and some 

 other substances exert the opposite effect. In- 

 creasing the concentration of a salt usually exerts 

 a different effect upon the curves of transpiration 

 and of growth. 



The Peg of the Cucurbits: William Ceockee, 

 University of Chicago, Chicago, 111., and Lee 

 I. Knight, University of Illinois, Urbana, 111. 

 The peg of the cucurbits is a parenchymatous 

 outgrowth between the root and the stem which 

 aids in the removal of the coat during germina- 

 tion. In the Hubbard squash and some other 

 forms all seedlings produce ring-like pegs approxi- 

 mately equal on all sides (or at least on the two 

 broader faces) if arching and contact are avoided. 

 Under similar conditions in the Big Tom pumpkin 

 and a number of other cucurbits a considerable 

 per cent, of pegless seedlings appear. The func- 

 tioning of this organ is possible only by its devel- 

 opment on the concave side of the arch. The one- 

 sided development is determined by the arching 

 (including perhaps the growth strains preceding 

 the actual arching) of the hypocotyl. Two stimuli 

 aid in the production of the arch-contact of the 

 coats and gravity. The contact of the coats is by 

 far the more effective, for it will induce very sharp 

 arching even against gravity. Gravity, independ- 

 ent of contact, gives strong enough arching to 

 produce only one-sided pegs in all seedlings when 

 the seeds are deviated 170° from the (point down- 

 ward) vertical position. There is no evidence, 

 contrary to the conclusion of Darwin, Noll and 

 others, that gravity directly stimulates the lateral 

 placement of this organ. 



The Effect of Illuminating Gas and its Con- 

 stituents on Carnations: Lee I. Knight, Uni- 

 versity of Illinois, Urbana, 111., and William 

 Ceockek, University of Chicago, Chicago, 111. 

 The flowers of the carnation are extremely sen- 

 sitive to traces of illuminating gas in the air, 

 while the vegetation is comparatively resistant. 

 In the Boston Market and pink Lawson varieties 

 three days' exposure to 1 part in 40,000 kills the 

 young buds and prevents the opening of those 

 already showing the petals. The buds of medium 

 age are considerably more resistant. In the same 



