19 iq] current literature 513 



Botanists will be glad to have the author's assurance that a more extended 

 and technical account of the living cycads is in preparation. In the present 

 pocket volume of 172 pages the author has done a useful piece of work and 

 has done it well. — M. A. Chrysler. 



NOTES FOR STUDENTS 



Inheritance in Pediastrum. — Practically all of our present knowledge of 

 inheritance in the plant kingdom is based upon work done with flowering 

 plants, regularly involving the sex act. The sex act in flowering plants, 

 furthermore, is peculiarly obscured; we cannot be altogether certain what 

 happens between the time of pollination and seed germination. We think 

 that the program followed is a remarkably regular one, but we feel that fre- 

 quently irregularities may occur, and we know that sometimes they do. We 

 wish therefore to know what all of these irregularities are, how they affect 

 inheritance, and how they may be induced or controlled artificially. It has 

 long been felt that a study of inheritance in simple plants would be suggestive, 

 for in them many of the complexities surrounding reproduction are stripped 

 away. The sex act takes place "in the open," so that there is more hope of 

 absolute control; some forms even he "below the level of sex," furnishing 

 unusual material for "pure line" work; and germ plasm seems identical with 

 body plasm. The direct bearing of such a study upon practical genetics may 

 be negligible, but upon theoretical genetics it promises to be profound. 



Harper^ has been working with cultures of Pediastrum, and has developed 

 some very significant ideas. He considers 3 "degrees of directness" of inheri- 

 tance in Pediastrum: (i) direct transmission, as by division of plastids; (2) the 

 more indirect transmission of those adult cell characters (as cell form) which are 

 not visibly present as such in the germ cell; (3) the entirely indirect transmis- 

 sion of the characters of the many-celled organism as a whole (as colony form). 

 The adult cell characters which Harper observed "do not suggest the working 

 out of influences emanating from elements in the chromosomal organization of 

 the nucleus, but rather the direct expression of the organization of the cell as 

 a whole when it begins to grow," involving specific polarities, surface tension, 

 etc. These cell characters come into expression whether or not the colony is 

 successfully formed. Colony characters, therefore, are dependent upon 

 individual cell characters, rather than the reverse. "If in the swarming period 

 the cell does not achieve its normal position .... the maladjustment is 

 never overcome." 



Thus the author paints for us two distinct pictures, which should be 

 considered separately. First, the picture of inheritance through specific 

 polarities, etc., of protoplasts as a whole, rather than determiners located on 



^ Harper, R. A., Organization, reproduction, and inheritance in Pediastrum. 

 Proc. Amer. Phil. Soc. 66:375-439. pis. 5, 6. figs. 54. 1918. 



