1919] AGRICULTURAL BOTANY. 431 



It is stated that pollen grains of the four species of Nicotiana employed 

 herein, as previously, germinated freely on many artificial media as well as on 

 the stigmas of the plants, but that they reached only a fraction of the length 

 attained under normal conditions, the growth moreover being abnormal. The 

 pollen tubes produced after selling were five to ten times as numerous as 

 required to fecundate the ovules. Pollen tubes after selling are indistinguish- 

 able in size from those following a cross. Variations in length of pollen tubes 

 after self-pollination and cross-pollination seem to be due wholly to differences 

 in the rate of germination of the pollen grains or to environment. Pollen tubes 

 produced after self-pollination grow at a uniform rate, and to all appearances 

 normally, but too slowly to reach the ovary before the flower decays. After 

 a compatible cross the growth of the pollen tube is rapid and accelerated. The 

 corresponding curve when plotted suggests an autocatalytic reaction. Cross- 

 sterile combinations resemble selfings as regards rate of pollen tube growth. 

 Near the end of the flowering season the rate of growth of self-pollen tubes 

 becomes more rapid, though little evidence has been obtained of acceleration 

 during their passage down the style. 



These results are thought to show that pollen tubes in a selfed pistil are not 

 inhibited in their growth by substances secreted in that pistil, but that sub- 

 stances are secreted in the pistil after a compatible cross which accelerate 

 growth. The direct cause of this secretion is a catalyzer, which the pollen-tube 

 nucleus is able to produce because the zygotic constitution of the plant produc- 

 ing it is different in certain particular hereditary factors from that of the plant 

 on which it is placed. 



The behavior of the chromosomes in fertilization, K. Sax (Oenetics, 3 

 (1918), No. 4, pp. 309-327, pis. 2). — The purpose of this study was to consider 

 not only the behavior of the chromosomes of the gametic nuclei, but also in the 

 triple fusion, which is considered as comparable to the union of the gametic 

 nuclei so far as inheritance of endosperm characters is involved. The ma- 

 terial was obtained from about 4,000 cases of fertilization in FritUlaria pudica 

 and 200 in Triticum durum hordelforme, both of which furnish a complete 

 series of stages in the first division of the fertilized egg. The behavior observed 

 in each of these plants is detailed with discussion. 



The segregation of CEnothera brevistylis from crosses with <E. lamarcki- 

 ana, B. M. Davis {Genetics, 3 (1918), No. 6, pp. 501-533, figs. 7). — An account of 

 studies carried on during 1916 and 1917 with species of (U. hrevistylis and 

 CB. lamarckimm and their crosses, direct and reciprocal, is given with results 

 which are tabulated and discussed. 



It is stated that the Fi generations of reciprocal crosses between these plants 

 are uniform and essentially indistinguishable one from another. The F2 gen- 

 erations from reciprocal Fi hybrids present a perfectly sharp segregation of 

 hrevistylis plants from lamarckiana in proportions approximating the mono- 

 hybrid Mendelian ratio of 1:3, the distinguishing characters of hrevistylis 

 being inherited in closely associated relations (behaving as a unit). Other 

 observations are detailed with discussion. The breeding data indicate that 

 crosses between hremstylis and lamarckiana result in a simple monohybrid 

 situation. 



Twin hybrids of CEnothera hookeri, H. de Vries (Genetics, 3 (1918), No. 5, 

 pp. 397-421). — Having been convinced by recent studies cited that lethal factors 

 and hybrid mutants play a considerable part in the splitting phenomena which 

 accompany the normal mutations of many species of Oenothera, the author 

 outlines the steps leading to this view and studies in connection therewith. 



Summarizing the data and conclusions of this work, he states that (E. hookeri 

 produces a splitting la^ta and a uniform velutina in its crosses with (E. grandi- 



