April 25, 1913] 



SCIENCE 



637 



"middle terrace" in the deltas of various wadis. 

 On physiographic grounds it seems to the re- 

 viewer open to question whether this terrace 

 should be put at this time or much later. 



Eiss-Wtirm or last Interglaoial Epoch. Mediter- 

 ranean Sea at present level, climate approach- 

 ing that of to-day. 



Wiirm Glacial Epoch. No notable expansion of 

 the Dead Sea. Formation of lowest terrace of 

 the valleys, a conclusion which is open to ques- 

 tion. 



Post-Glacial Epoch. Uniform prevalence of con- 

 ditions like those of to-day. 



In the interpretation of rock geology, Dr. 

 Blackenhorn is an expert, but when it comes 

 to the interpretation of such physiographic 

 phenomena as strands and terraces we are un- 

 able to accept his conclusions. In the first 

 place he has failed to observe a large num- 

 ber of lacustrine strands which close study 

 reveals at many points and at many altitudes 

 around the Dead Sea. In the second place, 

 he seems to have confused lacustrine and al- 

 luvial terraces in various places, and in the 

 third place he has correlated terraces which 

 apparently have no relation to one another. 

 For instance, on page 139, when describing 

 the Araba south of the Dead Sea, he de- 

 scribes a " Haupt Terrasse " with a height of 

 4 meters and a " Mittel Terrasse " with a 

 height of one meter. The first of these ter- 

 races is assumed to have existed ever since the 

 Mindel glacial epoch, and is correlated with 

 a terrace which elsewhere is 150 meters 

 high. He supposes the middle terrace to 

 have originated during the Riis Glacial 

 Epoch, and to have survived the vicissitudes 

 of the Riis-Wiirm Interglacial Epoch, the 

 Wiirm glacial epoch, and the succeeding 

 period during which the climate is supposed 

 to have remained in its present condition. 

 Both of these terraces, it must be remembered, 

 are in unconsolidated gravelly alluvium. It 

 seems to the reviewer that they probably are 

 the result of late post-glacial climatic pulsa- 

 tions. 



In view of the diversity of results ob- 

 tained by Dr. Blackenhorn and by other ob- 

 servers the whole question of the history of 

 the Dead Sea from tertiary times onward 



needs a far more thorough and systematic ex- 

 amination than it has yet received. This is 

 the more necessary since the Dead Sea and 

 Jordan Valley contain one of the best of aU 

 records of the Pleistocene history of the drier 

 portions of the world. Dr. Blackenhorn's ex- 

 cellent study of the fundamental rock struc- 

 ture of the region is an admirable basis for 

 such an examination. It is to be hoped that a 

 further step may soon be taken and that by 

 means of a careful instrumental survey of the 

 old strands, terraces and deposits, the physical 

 history of the region during the last hundred 

 thousand years or so may be conclusively de- 

 termined. Ellsworth HuNTmoTON 



SPECIAL ABTICLES 



THE PERFECT STAGE OP CYLINDOSPORIUM ON 



PRUNUS AVIUM 



In the fall of 1910, at the suggestion of Pro- 

 fessor George F. Atkinson, the writer began a 

 study of Gylindrosporium, as it occurs on 

 species of Prunus in the region of Ithaca, 

 N. T., in order to discover the life history, 

 and the relationship of the organism on the 

 different hosts. 



Several sweet cherry trees, which had been 

 severely attacked by Cylindrosporium during 

 the previous summer, were noted and the fallen 

 leaves observed at intervals for the appear- 

 ance of an ascogenous fungus. Early in 

 March developing fruit bodies were noticed in 

 abundance on many leaves, some of which 

 were brought into the laboratory and placed 

 in a moist chamber. After a few days at the 

 room temperature of the laboratory many of 

 the fruit bodies showed mature asci. 



Subsequent observations showed that a 

 stroma begins to develop under the Cylindro- 

 sporium acervuli about the last of August. 

 About the time of leaf fall the acervulus is cut 

 off from the underlying stroma by a compact 

 layer of host tissue two or three cells thick, of 

 thick-walled cells which surrounds the whole 

 stroma and very soon turns black. Slow in- 

 ternal development of this stroma continues 

 during the winter; and by the first of May 

 mature asci and ascospores may be found. 



