BOOKS AND CURRENT LITERATURE 91 



possible time. Of course the earliest fauna and flora we know may 

 have been preceded by many of which we have no record.] There 

 are many similar instances. 



Examples of omission — exoskeleton of earthworm and the cutic- 

 ular lining of stomodaeum not mentioned; the valves in the blood 

 vessels of the earthworm are not mentioned; polymorphism in hy- 

 droids and the character of medusae, if mentioned at all, should at 

 least be figured; the water currents in the branchial chambers of the 

 Crawfish are insufficiently described. Many other examples of in- 

 sufficient treatment might be given. 



But I must not prolong this detailed list of defects. Over one hun- 

 dred and twenty-five were noted in a hasty reading. Of these I have 

 mentioned here only a few instances of three of the many types of such 

 defects. The main criticisms of the book are for inaccuracy and lack 

 of clearness due to carelessness, for failure to approach the several sub- 

 jects in a way natural and fully intelligible to a beginning student, 

 in some instances for poor choice of and arrangement of material, and 

 for insufficient development of some themes. It is difficult to see 

 why Professor Calkins should care to write the book at all if he were 

 not ready to give to it the attention necessary to success. To properly 

 supplant the older work of Sedgwick and Wilson the book not only must 

 be more carefully written but must also be better planned. Few men 

 could do this better than Professor Calkins if he really cared to do it. 



Maynard M. Metcalf. 



Abscission. — The autumnal fall of leaves is the most generally 

 known example of abscission. However other plant parts may be 

 shed, among which may be mentioned embryo plants, as is the case in 

 viviparous species of Rhizophora, Podocarpus, and Tillandsia, stem seg- 

 ments which often include large branches, as in Salix, Popidus, and 

 Castilloa, tendrils, as in Ampelopsis, bud scales and stipules, spines, as 

 in certain cacti, flowers and their parts, and fruits, the most classic ex- 

 amples of which, perhaps, are cotton squares and bolls. Various in- 

 vestigations have recorded the occurrence of shedding and have sought 

 to explain the causes of abscission. Two recent papers by Lloyd 2 - 3 

 not only bring together these results but very materially contribute to 

 our knowledge of this interesting phenomenon. Attention is given to 



2 Lloyd, F. E., Abscission. The Ottawa Naturalist 28: 41-52, 61-75, 1914. 



3 Lloyd, F. E., Injury and abscission in Impatiens sultani. Sixth Rep't. 

 Quebec Soc. Protection of Plants, 72-79, PI. 1, 1914. 



