February 27, 1914] 



SCIENCE 



307 



smaller or larger portions of the originally 

 all-pervading sporogenous tissue. The 

 amphibious type of alternation of the 

 mosses and ferns has arisen, according to 

 Bower's conception, with the migration of 

 these plants to the land, and the assumption 

 of the terrestrial habit by the sporophyte. 

 The antithetic view was also supported in 

 a most striking way, later, by the results 

 of the workers on chromosomes. 



The homologous view of alternation also 

 has not been without supporters in the 

 years since Pringsheim. One of its up- 

 holders, Klebs (1896), based his belief on 

 the fact that he could determine the type 

 of reproductive cells formed by the alg£e 

 Hydrodictyon and Vaucheria, by changing 

 the conditions under which they are grown. 

 Lang (1896-98) favored the homologous 

 view because of the discoveries of Parlow, 

 de Barry, Bower, Farmer and himself on 

 apogamy and apospory. Scott, one of the 

 strongest advocates of the homologous alter- 

 nation theory, bases his belief not only on 

 the evidence afforded by the cases of apog- 

 amy and apospory, but also on the fossil 

 record. He points out the lack of any 

 sporophyte, living or fossil, that can be re- 

 garded as ancestral to that of the ferns. 

 In arguing for the homologous origin of 

 the leafy fern sporophyte from a liverwort- 

 like thallus Scott says (1911) : 



We know plenty of intermediate stages between 

 a thallus and a leafy stem; but no one ever saw 

 an intermediate stage between a sporogonium and 

 a leafy stem. 



v. THE DISCOVERY OP CHROMOSOME REDUC- 

 TION AND OF SYNAPSIS, 1888- 



We have seen that during the two dec- 

 ades at the middle of last century students 

 of sexuality in plants devoted their atten- 

 tion to the discovery of the relation of the 

 poUen tube to the origin of the embryo. 

 The three decades after 1860 were given 



largely to the proof of a union of a pater- 

 nal with a maternal nucleus as a constant 

 feature of the sexual process in plants. For 

 the past two decades workers interested in 

 reproduction have been engaged especially 

 in determining the behavior and fate, in 

 the various phases of plant development, 

 of those essential elements of the nuclei, 

 the chromosomes. The result of this study 

 has been to give us a much more definite 

 criterion than we had before, of just what 

 constitutes a sexual process. Moreover, this 

 intimate examination of the chromosomes, 

 together with the precise means of germi- 

 nal analysis by breeding, introduced by 

 Mendel, has given us some insight into the 

 significance of the sexual process in the 

 ontogeny and phylogeny of plants. 



The discovery of chromosomes in plants 

 may best be attributed to Strasburger, who, 

 in 1875, first figured them distinctly in 

 the embryo of Picea. It is true that Hof- 

 meister (1867) had noticed the equatorial 

 plate of "albuminous clumps" in cells at 

 the time of their division, and Russow 

 (1872) saw, in the dividing spore mother- 

 cell nuclei of Ophioglossum, plates of ver- 

 miform rods ("Stabchenplatten"). Stras- 

 burger (1879) and Hanstein (1880) and 

 Flemming (1880) were, however, the first 

 to realize the constancy of the occurrence 

 of chromosomes in the dividing plant 

 nucleus. The fact soon pressed itself upon 

 investigators that the number of these 

 chromosomes differs in different plants, 

 and in different phases of the same plant. 

 Then followed the epoch-making discovery 

 of the zoologist Van Beneden (1883), that 

 the number of chromosomes in the egg and 

 sperm of Ascaris is the same, and that the 

 double number characteristic of the body 

 cells becomes reduced during the maturing 

 of the germ cells. Botanists after some de- 

 lay, due, as Strasburger says, to lack of 

 proper technique, succeeded in demonstrat- 



