CYTOPLASMIC HEREDITY 419 



tip by both genom and plasmon, and the length of the mid-rib almost 

 wholly by the plasmon.^ 



Other Cases. — In a few higher plants it has been shown that certain 

 characters, notably sterility, are determined in part by some element or 

 condition in the cytoplasm. For example, certain reciprocal hybrids in 

 Epilobium show differences in fertility which indicate an interaction of 

 genes and unlike maternal cytoplasmic elements.^" A somewhat similar 

 situation is found in Linum. In crosses between two varieties of Vicia 

 Faba, major and minor, certain genes are found to produce different 

 effects in the cytoplasms of the two varieties. This is also observed in 

 reciprocal crosses of Nicotiana Langsdorffii and N. Sanderce.'^^ In a 

 certain race of Zea Mays wdth pollen which degenerates, usually after the 

 division forming the generative cell, it has been shown by an extensive 

 series of crosses that the peculiarity is due directly to something in the 

 cytoplasm and is not affected differentially by known genes in the various 

 linkage groups. Moreover, the sterility is not transmitted by pollen 

 from partially sterile plants. The cytoplasm in the sporocytes differs 

 visibly in sterile and non-sterile individuals, but the real nature of the 

 difference is not known. ^^ In a fungus, Pholiota mutahilis, mycelia may 

 be obtained from a cell having a nucleus of one strain in a mixture of 

 cytoplasms from two strains, and these mycelia may produce fruit 

 bodies. The form of these fruit bodies is affected by the cytoplasm, the 

 various gradations between the forms of the parental strains varying 

 apparently with the proportions in which the parental cytoplasms are 

 mixed (Harder, 1927). 



The larval characters of certain animals should be mentioned here. 

 The mature egg, notably in echinoderms, ascidians, and certain other 

 groups, exhibits a visible cytoplasmic differentiation, and by virtue of 

 this fact develops for a time in a definite manner irrespective of the type 

 of sperm causing its activation. Among the characters appearing in the 

 early stages of embryogeny are some which are inherited in each genera- 

 tion from the mother only, since their differentiation is actually under 

 way in the cytoplasm before syngamy occurs. If this " promorphology " 

 of the egg and therefore such embryonic characters are under the differen- 



^ When the effect is produced chiefly by the genom, the genom is said to be ante- 

 cedent and the plasmon recedent; when it is due mainly to the plasmon, the latter is 

 antecedent and the genom recedent (von Wettstein, 1926; p. 260). 



i^Lehmann (1918 et seq.), Schwemmle (1924), Lehmann and Schwemmle (1927), 

 Renner and Kupper (1921), Michaelis (1929). 



" Chittenden and Pellew (1927) and Chittenden (19276) on Linum, Sirks (1931) 

 on Vicia, East (1932) on Nicotiana. 



12 Rhoades (1931a, 1933). The distribution on the cob of kernels producing sterile 

 and non-sterile plants rules out the hypothesis of a somatic segregation of a small 

 number of elements (c/. Anderson, 1923, and Demerec, 1927, on chlorophyll 

 characters). 



