June 5, 1914] 



SCIENCE 



835 



in the vicinity of Ithaca, N. Y. They differ by 

 more than thirty easily recognizable contrast pairs 

 of ' ' unit characters, ' ' or alleloniorphic pairs, or, 

 in terms of the "presence and absence" hypoth- 

 esis, there are more than sixty ' ' factors ' ' of recog- 

 nizable characters which meet in the fertilized egg 

 of the cross between the two parents. These char- 

 acters relate to the habit and color of the adults ; 

 features of the rosettes, foliage and inflorescence. 



When pycnoearpa is the mother two distinct hy- 

 brid types are segregated in the first generation, 

 and have been brought to maturity. These are 

 twin liyirids. When nutans is the mother the 

 same twin hybrids appear, and in addition a trip- 

 let which at present is in the rosette stage. 



An analysis of the hybrids shows a distinct link- 

 ing, or association, of certain characters. The 

 bond between these characters is stronger than that 

 of the total composition of either parent, and in 

 the ease of certain characters stronger than the 

 total composition of certain organs or members. 

 This results in a splitting of the total composi- 

 tion of both parents, and also a splitting of the 

 total composition of certain members of the plant 

 body. Examples of this linking of characters are 

 as follows: First, habit characters; second, color 

 characters; third, petal characters; fourth, broad- 

 ness and toothedness of rosette leaves; fifth, nar- 

 rowness and cutness of rosette leaves; sixth, 

 crinkledness, convexity and red-veinedness of ro- 

 sette leaves; seventh, plainness, furrowedness and 

 white-veinedness of rosette leaves. 



This splitting of the parental constitution re- 

 sulting in the segregation into twin and triplet 

 hybrids in the first generation occurs in the zygote 

 or fertilized egg. Therefore it is of a very differ- 

 ent type from that which takes place in Men- 

 delian segregation due, according to general be- 

 lief, to a qualitative, or differential division or 

 reaction, in the gonotokonts (mother cells of the 

 pollen grains and embryo sac). No such qualita- 

 tive division is known to take place regularly in 

 the fertilized egg. Therefore the usual karyoki- 

 netie process in the first division of the zygote can 

 not be invoked in an interpretation of segrega- 

 tion of ' ' unit characters ' ' in the fertilized egg. 

 The following hypotheses are considered. 



First. De Vries's hypothesis of twin hybrids 

 from mutating species. It does not appear prob- 

 able, in the case of the two species considered 

 here, that the segregation is due to the mutating 

 character of one parent with its consequent splita- 

 bility of constitution, combined with the splitting 

 power of the constitution of another non-muta- 



ting parent, which is de Vries's interpretation of 

 twin hybrids in the first generation of a cross 

 between (E. lamarckiana, or certain of its mu- 

 tants, and a wild non-mutating species. 



Second. Theory of a differential division in the 

 zygote. The meeting, in the fertilized egg, of 

 such a large number of homologous, but contrast- 

 ing, ' ' qualities " or " bearers, ' ' may be less favor- 

 able for a blending of the contrasting members of 

 a pair, than for some other combination. The 

 different positions which the linked "factors" 

 or "qualities" occupy as they approach the 

 nuclear plate of the first division may well be due 

 in a large measure to chance. In this way dif- 

 ferent combinations might establish a working 

 relation in different eggs. The material repre- 

 senting the groups of characters not entering into 

 any one working combination may then be left 

 behind in the first suspensor cell of the embryo, 

 or cast out into the cytoplasm. The material in 

 the first suspensor cell plays no part in the forma- 

 tive processes of the new individual, since this 

 cell is side-tracked by the basal wall formed dur- 

 ing the first division of the zygote. 



Third. The reaction theory. In view of the 

 fact, which seems to be now quite well established, 

 that certain hereditary qualities are governed by 

 enzymatic action, it may not be improbable that 

 all the factors, or bearers, may work through 

 enzymatic or catalytic or other chemical processes. 

 But when the substances mixed are alike in all 

 cases, and the conditions are the same, it is not 

 intelligible, from a chemical point of view, why 

 in some eggs one reaction should take place, while 

 in others the reactions should be totally different. 

 Even if we accept in principle the reaction 

 theory, the different reactions taking place in 

 different hybrid eggs seem to point to a differen- 

 tial division or segregation of material portions 

 or regions of the hybrid egg cell. 



The Vegetation of the Sargasso Sea: William G. 



Farlow. 



The Sargasso Sea through which Columbus 

 passed on his first voyage to America is charac- 

 terized by the scattered masses of gulf weed which 

 float on the surface of the ocean in patches gen- 

 erally from fifty to a hundred feet in diameter. 

 The question as to the origin of the gulf weed 

 has never been definitely settled. Some consider 

 that the gulf weed whose botanical name is Sar- 

 gassum iacoiferum is merely a mass of sterile 

 branches of some species of Sargassum which 

 grows attached in the region of the West Indies 



