igi2] CURRENT LITERATURE 433 



published observations on the mallow rust. According to him the mycelium 

 of the fungus lives through the winter in the stems and petioles of Malva 

 rotundifolia, but the teleutospores do not survive the winter in Michigan. 



Although Eriksson's observations have added many facts to those already 

 known of the general biology of the mallow rust, his conclusion that the fun- 

 gus lives through the winter only in the form of a mycoplasma in the seed or 

 young plant is largely inferential, and one is inclined to give preference to the 

 explanations of Taubenhaus and of Dandeno as less at variance with general 

 experience than is the mystical mycoplasma. — H. Hasselbring. 



Germination. — The irregularity of the differences in rapidity and per- 

 centage of germination in the unlike seeds of heterocarpic plants under various 

 conditions of germination, when the fruit and seed coats are left intact, is well 

 shown in a lengthy paper by Becker, 10 who studied in a rather superficial way 

 the germination of 47 species of Compositae, several Cruciferae, and three 

 Chenopodiaceae. Morphological position, the sexual condition of the flowers, 

 darkness, temperature, increased and decreased oxygen pressure, nitric acid, 

 and Knop's solution influence now disk seeds, now ray seeds, or both, or 

 neither according to species, apparently without regularity. Age and possible 

 sterility of the seeds are disturbing factors in the results. Most of the experi- 

 ments were performed with fruit coats intact, but enough were removed to 

 prove that the inclosing structures are largely responsible for these differences, 

 which always become much less on removal of the fruit coat. These differ- 

 ences in germination do not, therefore, as Ernst, and Correns assumed, rest 

 on differences in the constitution of the embryos. This fact has been recog- 

 nized here for some years, but has not been properly recognized abroad. 

 Embryos of dimorphic seeds may and do differ, as the reviewer has shown 11 for 

 Xanthium; but the differences due to embryos alone cannot be determined 

 with seed coats left on the seeds. With Axyris amaranthoides Becker does 

 not get total failure of the round seeds to germinate, as did Crocker" with 

 seeds of this plant from our northwest, but merely a very low germination. 

 This may be due to ecological differences in the regions where the plants grow 

 affecting the seed coats. 



As to the influence of increased oxygen, Becker finds that brief exposure 

 of seeds brings about the same kind of response as continuous exposure to 

 high oxygen pressures, and argues therefrom that it exerts a chemical stimulus 

 upon the protoplasm of the embryo, rather than increases the respiration as 

 Crocker has suggested. Becker does not tell us what is the difference 



10 



bei 



derselben Species. Inaug. Diss. pp. 7-129. 191 2. 



11 Shull, Chas. A., The oxygen minimum and the germination of Xanthium 



seeds. Bot. Gaz. 52:453-477. 191 1. 



12 



germination. Bot. Gaz. 42: 265- 



291. 1906 



