466 



SCIENCE. 



[N. S. Vol. XVII. No. 429. 



entirely disappeared from the nodes of the 

 reproductive axis. 



Briefly, the author's hypothesis is that 

 the primitive monocotyledon was a seg- 

 mented plant, composed of phytomeres, 

 and characterized by the presence of con- 

 centric bundles at the nodes. Probably 

 as the result of periodically recurring 

 unfavorable conditions of existence, the 

 primitive segmented type of stem became 

 differentiated into vegetative and repro- 

 ductive portions of very different struc- 

 ture. The vegetative part of the stem 

 gradually became characterized by tufted 

 leaves and short internodes, resulting 

 finally in the fusion of the nodal segments, 

 containing concentric bundles to form a 

 continuous system. In the reproductive 

 axis of the lover groups of Monocotyle- 

 dons, on the other hand, the ancestral divi- 

 sion of the stem into distinct phytomeres 

 is retained, together with the recurring 

 segments of concentric bundles. In the 

 higher monocotyledons, however, the primi- 

 tive organization disappears and concentric 

 bundles are no longer found in the repro- 

 ductive axis. 



The hypothesis outlined above is based 

 on the study of a considerable number of 

 facts, and, further, seems to gain force 

 from two considerations. In the first 

 place, it agrees on the whole very well with 

 the data supplied by a study of the floral 

 organs. Secondly, a typical cambium has 

 been found in the reproductive axis and 

 seedlings of some of the lower monocotyle- 

 donous orders mentioned above. The latter 

 feature is reserved for subsequent consid- 

 eration, but it may be pointed out that this 

 discovery lends support to the opinion re- 

 cently expressed by Queva, in connection 

 with his anatomical studies on the Uvul- 

 ariaceffi, viz., that the Monocotyledones are 

 derived from the Dicotyledones, or an 

 equivalent stock, by the loss of a cambium 



and an increase in the number of leaf- 

 traces. W. F. Ganong, 



Secretary. 



8GIENTIFI0 BOOKS. 

 Morphogenetische Btudien. Als Beitrag zur 



Methodologie Zoologischer Forschung. By 



Tad. Gabeowski. Gustav Fischer. 1903. 



Gabrowski publishes under the above title 

 a quarto monograph of which the first 24 

 pages deal with the structure of Trichoplax 

 adhcerens, 9 pages with the biology of this 

 animal, and 141 pages of general discussion. 



In regard to the structure of Trichoplax 

 very little that is essentially new is added. 

 The organism is disc-shaped and, as a rule, 

 irregular in outline. It has an outer layer 

 of ciliated ectoderm, and an internal spongy 

 parenchyma. It lacks completely digestive 

 tract, reproductive organs and nervous sys- 

 tem. Some of the parenchyma cells, although 

 not differentiated into muscles, are probably 

 contractile, and cause the changes in the shape 

 of the body. 



Trichoplax moves slowly over solid bodies 

 by means of the long cilia on its under sur- 

 face. No food particles of any sort have ever 

 been found in the body, and the author's only 

 suggestion is that the food may be soluble 

 organic matter absorbed from the surround- 

 ing water; but this is purely conjectural, and 

 nothing new was discovered as to the prob- 

 able source of food. 



Reproduction is by division into two pieces; 

 the body drawing away in two directions until 

 the connecting part is finally broken. Ga- 

 browski has also seen two, and even three, 

 individuals come together and fuse into a 

 single mass, for which process he suggests the 

 use of the term concrescence — a term that 

 has acquired a very different meaning, and it 

 seems unfortunate to apply it to this process 

 of fusion. 



A long discussion of the affinities of Tricho- 

 plax leads the author nowhere, since no new 

 facts of any significance have been added by 

 his work and the speculation is not particu- 

 larly illuminating. Even less impressive is 

 the long, heavy discussion of the gastrula 

 theory which is painfully dragged through 



