606 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Pollen of Hybrids* — Herr A. Jencic has carried out a series of 

 experiments with the view of settling the much disputed point of the 

 relative fertility of hybrid plants, and especially of tbeir capacity for 

 producing fertile pollen. In 33 living and 10 dried species, he finds 

 the law universal that the fertility of the pollen is diminished in hybrids, 

 but the degree of reduction varies greatly. In some cases no pollen at 

 all is produced, while Orchideae exhibit but a very small reduction of 

 fertility ; and between these extremes there are all intermediate grades. 

 Hybrids between nearly related species were always found to be more 

 fertile than those between species le!?s nearly related. Pollen-grains 

 which did not swell up in water were regarded as sterile. 



Descendants of Race-Hybrids. f— Commenting on De Vries's paper 

 on the law of splitting of hybrids, Herr C. Correns points out that the 

 same results were obtained by Mendel in 1866, and precisely the same 

 explanation offered. The descendants of hybrids reproduce every pos- 

 sible combination of the distinguishing characters of the parent-forms ; 

 but these characters are not in any sense weakened. 



(2) Nutrition and Growth (including 1 Germination, 

 and Movements of Fluids). 



Formation of Chlorophyll in the Seedlings of Gymnosperms.J — 

 From a series of experiments carried on by Herr A. Burgenstein on the 

 formation of chlorophyll in the seedlings of Gymnosperms in the light 

 and in the dark, he comes to the following general conclusions. Seed- 

 lings of ConiferaB (except Salisburia, and Ephedra among Gnetaceaa) 

 become green when light is entirely excluded ; but more intensely at a 

 favourable temperature (15 c '-25° C.) than a lower one (5°-10°). Cycas 

 and Zamia, and probably all Cycadeae, do not develope chlorophyll in 

 their seedlings, even at an optimum temperature, in the complete absence 

 of light. The formation of chlorophyll takes place not only in the coty- 

 ledons, but (except in Larix) also in the hypocotyl. In the Araucarieaa a 

 number of green leaves are developed on the stem which springs from the 

 growing point, even when light has been excluded for weeks. The for- 

 mation of chlorophyll is not confined, as it is in other Coniferae, to the 

 cotyledons. In many Coniferae, especially species of Abies and Gedrus, 

 the embryo contains chlorophyll even in the dormant seed. When this 

 is not the case, the seedling begins to turn green even within the testa, 

 before or after it is broken through by the radicle. The endosperm is ab- 

 sorbed more slowly, and the epinastic expansion of the cotyledons is less 

 complete in the dark than in the light. Seedlings of Coniferae and 

 Gnetacese which have developed in the dark form shorter roots and coty- 

 ledons, but larger and thicker hypocotyls, than those which develope in 

 the light, when the conditions are otherwise the same. The cells of the 

 hypocotyl are absolutely longer and their transverse diameter shorter in 

 the dark than when formed under the influence of light. 



* Chlorophyll Assimilation. § — Signor Pollacci states that the green 

 organs of plants grown in sunlight restore the colour of magenta which 



* Oesterr. Bot. Zeitschr., 1. (1900) pp. 1-5, 41-6, 81-6. 



t Ber. Deutsch. But. Ges., xviii. (1900) pp. 158-68. Of. this Journal, ante,-pA8-±. 



t Tom. cit.. pp. 168 84. 



§ Atti 1st. Bot. Pavia, vii. 1899. Sec Journ. Chem. Soc, 1900, Abstr. ii. p. 426. 



