408 REVIEWS. 



About this period peculiar thickenings are formed on the 

 walls of the cells composing the epidermis of the anther, all 

 the food plasma has been used by the pollen, and the grains 

 become " ripe." Sections show that the two nuclei found 

 in a younger stage gradually disappear and become dis- 

 tributed in the protoplasmic network. Strasburger believes 

 this to be important, since it explains why he and Elfving 

 failed to trace the nuclei into the apex of the pollen tube in 

 Angiosperms. 



In Malta the pollen grain may protrude many tubes ; 

 but Strasburger could not find that the nuclei suffer cor- 

 responding division. The facts appear to be simply that the 

 nuclear substance becomes distributed in the protoplasm, 

 and that, after passing over to the egg-cell, a reaggregation 

 occurs and a " nucleus" — the nucleus of the male element — 

 is found once more. 



The above remarkable results are further supported by 

 investigations of the pollen in GeraniacecB^ Gaurea, Clarkia, 

 Epilobiun, Cucurhitace(B, and many others, including several 

 Monocotyledo7is. Especially interesting results were afforded 

 by Cucurbita. 



From many points of view Strasburger's investigation of 

 the spores of vascular Cryptogams — Lycopodium, Osmunda, 

 Equisetum, Marsllea, and Salvinia, are of great importance. 

 We must, however, refer the reader to the book itself for 

 details, as also for the description of some points in connec- 

 tion with the lower Cryptogams, and pass on, meanwhile, 

 to notice the result of the author's investigations of the 

 starch grain. 



What may be termed the second division of the book is 

 presented under the following heading :rr-" Anlage und 

 Wachsthum der Stdrkekorner." We may conveniently, as 

 before, select one prominent example as illustrating the 

 chief results obtained. 



The large well-marked starch grains of PJiajus have 

 been well studied by Schimper, and Strasburger's descrip- 

 tion agrees essentially with his. Strasburger has also come 

 to the conclusion that the dark and bright layers, which 

 vary in breadth, «&c., are layers of apposition — that the dark 

 lines denote surfaces of adhesion, and are usually formed 

 between layers composed of many lamellae. Where a long 

 pause has ensued between the apposition of two layers, the 

 continued action of the environment has altered the outer 

 lamella; of the older layer ; this becomes evident by changes 

 in optical properties, &c. Similarly, the outermost layer of 

 all, which is also the most resistant, has been formed by 



