1909] CURRENT LITERATURE 169 



(5) heterozygotes; in the numerous cases where heterozygotes differ from either 

 parent, "the ability to transmit certain characters is correlated with other apparent 

 characters." Under gametic correlations are placed the phenomena of partial and 

 complete "coupling," so called, developed chiefly by Bateson. — R. R. Gates. 



Tyloses in ferns. — It has been noted by various writers that in the stems and 

 petioles of ferns the protoxylem groups suffer disintegration, and into the cavities 

 so formed the wood-parenchyma grows, forming the "cavity-parenchyma" of 

 Russow. Proliferations from these cells frequently fill the cavities, and present 

 the appearance of tyloses. These growths have recently been studied in detail by 

 two independent workers, Kirsch 21 and Miss McNichol. 22 Both writers show 

 that the phenomenon is widespread, being found in nearly every family of the 

 true ferns, as well as in Marsilia and the Ophioglossaceae. In both papers the 

 cells in question are carefully described and their origin as stated above is proven. 

 Kirsch has studied Pteris aquilina in most detail, and finds cavity-parenchyma 

 m the stipe and in all regions of the rhizome, where it occurs in the outer system 

 of bundles which he erroneously regards as cortical (p. 388). He offers the fol- 

 lowing as a theory of the cause of these growths: the cavity formed by disintegra- 

 tion of the protoxylem at first functions as a water duct; later the metaxylem 

 (secondary xylem according to Kirsch) makes its appearance and performs the 

 duty of water carrier. Hence the pressure in the cavity is reduced, and as a con- 

 sequence tyloses grow into it.— M. A. Chrysler. 



Composition of a field of maize.— A brief paper by Shuix^ calls attention 



to the view, already expressed by DeVries and others, that a field of corn, like 



wheat and other grains, is made up of a number of elementary species or biotypes. 



dlscusses th e fact that inbreeding in corn results in deterioration, and points 



°ut that the old hypothesis that the deleterious effects of inbreeding result from 



e accumulation of disadvantageous individual variations to form an organism 



j an inh armonious or unbalanced constitution, is untenable, in view of the 



*te of cleistogamy, self-pollination, and parthenogenesis in plants which have 



Gently been successful in the struggle for existence. A cornfield is conceived to 



a series of hybrids between elementary species, and on the basis of the common 



jervation that hybrids between nearly related forms are more vigorous than 



biot ParCnt ' hC believes that over-selection, which eliminates down to a single 

 °<ype t results in deterioration, not intrinsically from inbreeding, but because the 

 a er Vlg0r which comes from the crossing of biotypes has been eliminated. The 



stipe" K h RSCH ' SlM ° N ' ° n the development and function of certain structures in the 

 CanaH u , Zome of Pt ™ aquilina and other Pteridophytes. Trans. Royal Soc. 

 ^ 1IIl4 --353-4i2. figs. 27 + 2I . I0O7 . 



Botanv MCXlCHOL ' M - ° n cavit y Parenchyma and tvloses in ferns. Annals of 

 ■ ":4oi- 4 , 3 . pi. 25. loog. 



AsJShull, Geo. H., The composition of a field of maize- Amer. Breeders' 

 ^Mipp.e. i 0o8 . ^ 



eithe 





