Carothers: The Cell Mechanism 



3S3 



whether secondarily split or not, now 

 become arranged. Because of the 

 peculiar form and consistency of the 

 heterotype chromosomes the mitotic 

 figure presents a striking contrast in 

 appearance to the ordinary figure 

 of somatic cells." This "striking con- 

 trast," however, depends wholly upon 

 the fact that the chromosomes are 

 "secondarily split," that is, that they 

 are tetrads and not dyads. The 

 writer has had enough contact with 

 botanical material to be confident that 

 this statement is true for plants as well 

 as animals. A number of the more 

 recent plant cytologists have recog- 

 nized the tetrad nature of the chromo- 

 somes of the first maturation division. 

 The manner in which the chromo- 

 somes split, the existence of chro- 

 momeres, and the structure of the 

 first maturation chromosomes are all 

 matters of prime importance in cytol- 

 ogy and genetics and since this is a 

 book which, on account of its many 

 excellent qualities, is sure to be 

 largely used as a text-book, it becomes a 



clear duty to indicate these weaknesses. 

 However, a capable instructor with 

 suitable material for demonstration 

 may easily show the real conditions 

 and thus turn these points to advantage 

 in teaching students independence of 

 observation. 



In conclusion: this book seems 

 adapted to meet the needs of several 

 classes of people, among them the 

 general reader seeking to enlarge his 

 field of knowledge and the practical 

 breeder who wishes better to compre- 

 hend the physical mechanism through 

 which he obtains his results. The be- 

 ginning student of cytology should find 

 it interesting because of the emphasis 

 which is placed on the problems which 

 are now attracting most attention. The 

 instructor who wishes a text-book will 

 find the subject presented in a well- 

 rounded manner. While to the zoo- 

 logical cytologist, the book will be 

 especially useful since it stresses the 

 views of the botanists and makes their 

 results more readily accessible. — E. 

 Eleanor Carothers. 



The Improvement of Citrus Fruits 



That the study of bud variation in 

 plants, frequently thought of as the 

 harmless amusement of amateur hor- 

 ticulturists, has led to an increased 

 production of citrus fruits valued at 

 more than a million dollars annually, 

 is a fact that should be of more than 

 passing interest to the members of the 

 Genetic Association. 



In a recent paper, ^ Mr. A. D. Shamel 

 calls attention to the importance of this 

 method of improving our agricultural 

 plants and shows that a surprising 

 number of the leading varieties of most 

 of our perennials have originated as 

 bud sports or mutations. That Mr. 

 Shamel himself has taken a leading part 

 in this work and that it is chiefly 



through his efforts that the value and 

 importance of bud selection now is 

 being appreciated, is modestly con- 

 cealed. The paper gives a brief but 

 explicit description of the methods 

 that have been followed in the bud 

 selection work with citrus fruits. 



Mr. Shamel also announces that 

 preliminary work with sugar cane in 

 Hawaii gives definite indication that 

 a corresponding improvement in that 

 crop also may be brought about by 

 applying similar methods. The results 

 of bud selection in a great variety of 

 plants are brought out in a vivid and 

 striking way by the 41 beautiful 

 full-page illustrations. — G. N. C. 



1 "The Improvement of Plants Through Bud Selection," A. D. Shamel, Experiment Station of 

 the Hawaiian Sugar Planters' Asso., March, 1921. 



