January 12, 1917] 



SCIENCE 



47 



at times he assumed, as did Carnot, that 

 the quantities of heat entering and leav- 

 ing the cylinder of an engine, irrespective of 

 the performance of work, were equal. If for 

 the sake of completeness Holtzmann's work be 

 referred to in this volume, so too should that 

 of Marc Leguin (1839), who as far as the per- 

 formance of an engine is concerned anticipated 

 ■other workers (except possibly Rumford and 

 Davy) in a partial statement of the law of the 

 equivalence of heat and work. 



Had this volume been written by American 

 physicists, emphasis would have been placed 

 ■on parts of the subject not here noticed. 

 Wood on resonance spectra, ISTichols and Mer- 

 ritt on fluorescence. Miller, Webster, Sabine 

 on sound, Michelson on the rigidity of the 

 earth, Pupin, G. W. Pearce on wireless teleg- 

 raphy, would have been recorded. 



But when we come to view the great body 

 of philosophical thought which has come to 

 us in this past generation we must give to 

 Teutonic physicists credit for a large share. 

 Boltzmann's conception of the entropy of a 

 body in terms of the probability of state; 

 the extension by Planck of the idea of entropy 

 and temperature to radiation, leading to the 

 distribution of energy in the spectrum of a 

 full radiator and to the bewildering quantum 

 theory; Einstein's contributions to molecular 

 theory and to the theory of relativity — these 

 stand out as substantial portions of " Die 

 Kultur der Gegenwart." G. F. Hull 



SPECIAL ARTICLES 



PEANUT MOSAIC 



On September 28, 1915, while looking over 

 a field in which peanuts {Arachis hypogcea) 

 had been grovsm annually for the past six years 

 a plant was observed, one shoot of which bore 

 mottled leaves. A careful search of the entire 

 field was made, but no other plant bearing 

 mosaic leaves was found. This made the 

 writer suspect that the trouble was not infec- 

 tious. It seemed advisable to test this point 

 further, especially since the mosaic plant was 

 otherwise healthy except for a few leaf spots 

 produced by Oercospora personata. 



This mosaic plant was transferred to the 



greenhouse. Before final potting two of the 

 mature pods were removed from the plant and 

 opened, and four peas taken from them were 

 planted at once in a pot of greenhouse soil. 

 The four resulting plants together with two 

 other seedlings which came up later from peas 

 left on the mosaic plant, have been under ob- 

 servation during the past five months. In no 

 case have any signs of mosaic developed. It 

 would thus appear that this mosaic was not 

 carried by the seed. 



The transplanted mosaic plant continued to 

 grow and produce new leaves at the ends of 

 the shoots, but in no case did any but the 

 mosaic shoot produce new mosaic leaves. 



To obtain further data as to the infectious 

 nature of this mosaic a pot of four peanut 

 plants from a 1914 crop of seed was selected. 

 Two plants were slashed near the ends of the 

 shoots with a flamed scalpel to serve as checks. 

 The other two plants were treated in a similar 

 way, except that into the slashed stems bits 

 of macerated mosaic leaflet were inserted. 

 These plants have been under observation for 

 the past five months but no signs of mosaic 

 have developed on either the checks or inocu- 

 lated plants. 



On October 14, 1915, a pot containing pea- 

 nut plants from the 1914 seed was taken to the 

 laboratory. By means of India ink circular 

 areas were marked on each leaflet of one plant. 

 Within these circles the tissues were pierced 

 several times with a flamed dissecting needle. 

 This plant served as a check. The second 

 plant in the same pot was treated in a similar 

 way except that before piercing the leaf tissues 

 the needle was moistened in the juice from 

 mosaic leaflet freshly removed from the potted 

 mosaic plant. Similar checks and inoculations 

 were made on garden peas (Pisum spp.) grow- 

 ing in pots, using juice from the mosaic pea- 

 nut leaflet. On November 13, 1915, the above 

 plants were carefully examined, but neither the 

 checks nor the inoculated plants showed any 

 sign of mosaic on either young or old leaves. 



On ISTovember 13, 1915, to further test the 

 infectious nature of this peanut mosaic one 

 cheek was prepared by injuring each leaflet of 

 the plant by pinching it between the thumb 



