July 18, 1919] 



SCIENCE 



69 



engaged in broader forest study, especially in 

 tlie tropics, have felt the severest need for 

 ready or approximate identification by leaf 

 characters. Secondly, an adequate study of 

 fossil steins systematically collected, and in- 

 cluding "wherever possible to obtain, the cir- 

 cum-medullar region has never been even be- 

 gun. Thirdly, the signal success with which 

 Professor Ifathorst has developed a chemical 

 treatment of carbonized remains so that col- 

 lodion imprints of many histologic features 

 may be had, affords such an all-important fac- 

 tor of control that many of the longer known 

 floras require restudy as a whole, or in part by 

 this method. It is not probable that classifi- 

 cation can be safely based on features dis- 

 closed by the " chemical method " ; but as an 

 aid in determining genera or species it is ef- 

 fective, often in the case of rather fragmentary 

 material. Fourthly, the improved methods of 

 sectioning coals, and fragmentary stems like 

 those of the Kreischerville conifers, as devel- 

 oped by Jeffrey, indicate a great extension of 

 exact study following more searching collec- 

 tion afield. 



Under the circumstances we should have on 

 at least ten of our surveys, and in at least a 

 dozen of our larger universities thoroughly 

 equipped paleobotanists. And need I call at- 

 tention to the fact that the scientific require- 

 ments are severe? A good paleobotanist needs 

 geologic and paleontologic, as well as botanic 

 training, and above all things he needs to be 

 not merely an expert in the laboratory but a 

 rugged and determined field worker and col- 

 lector. Such men have to be given position. 

 Subsidiary activities, and foreshortened re- 

 sults, are apt to be near neighbors. Though 

 the comparison be invidious, it yet requires to 

 be made. In their larger collecting schemes 

 both the invertebrate and vertebrate paleon- 

 tologist constantly spend in collection and 

 reconnaissance sums such as have never been 

 even relatively available for work in the fossil 

 plants not one whit less important. 



In closing I would like to call attention to a 

 point of concrete value. According to the in- 

 terpretations of evidence which have thus far 

 had acceptance, there results a lack of forest 



making types from the Trias to the close of 

 the Jura. But if, as now seems apparent, the 

 cyeadeoids have a degree of angiospermous 

 affinity, the microphyllous forms must often 

 represent important elements in unrecognized 

 forests. If so, many of the forms probably had 

 the same capacity to thrive in temperate to 

 colder climates as the dicotyls they often ac- 

 company, especially in the puzzling associa- 

 tion noted by Hollick in the Kenai flora of 

 Alaska.^ This flora must have flourished near 

 to snow fields and glaciers. The cold presag- 

 ing the bipolar ice caps may therefore have 

 come on far earlier than has been hitherto un- 

 questioningly believed. This, with the new 

 methods of study, and especially the more per- 

 sistent scanning of the broader outlines of 

 plant succession, is only one of the many prob- 

 lems which await development of paleobotany. 



G. E. "WiELAND 



GRAVITATIONAL ATTRACTION AND URANIUM 

 LEAD 



To THE Editor of Science: As shown by 

 Professor Theodore W. Richards in his presi- 

 dential address,^ it has been found that the 

 last known disintegration product of the ura- 

 nium series, uranium lead, behaves in all re- 

 spects like ordinary lead, with the exception 

 that it is slightly radioactive and has an 

 atomic weight of about 206.1, as compared 

 with that of ordinary lead, 207.2. It has also 

 been found that lead derived from uranium 

 minerals usually shows some value between 

 the above limits and thus appears to be a mix- 

 ture of the two former kinds. None of the 

 many attempts made to effect a separation has, 

 however, met with success, nor has any theory 

 been advanced by which the discrepancies in 

 atomic weight, which seem quite without a 

 parallel among the other elements, may be 

 satisfactorily explained. 



The possibility suggests itself that the dis- 

 crepancies referred to might be due to a 

 slightly different behavior of the various forms 



1 ' ' The Problem of Eadioaetive Lead, ' ' Sci- 

 ence, January 3, 1919. 



2 See American Journal of Science, TV., 31, April, 

 1911, pp. 327-330. 



