170 CARROLL— ON DEVELOPMENT OF 



parts. In /. fulva the reduction affects the short style and stigma and 

 the number of ovules. In / noli-tangere five short styles per- 

 sist. The reduction of style and stigma is common in cleistogamous 

 flowers. Helene Ritzerow (41) lists some ten species where it occurs. 

 In Aspicarpa hirtella, Aspicarpa longipes and in Specularia a reduction 

 in the number of carpels occurs (41, p. 212). On the whole, however, 

 the pistil seems to suffer less reduction than do other parts of the flower 

 an cleistogamy, 



VI. Growth of Pollen Tubes and Fertilization 



On germinating the grains in sugar solution, four tubes begin growth 

 from the four corners of the somewhat barrel-shaped or elliptic pollen 

 grain. The behavior of the nuclei with respect to these four tubes was 

 not discovered. In the few cases examined of pollen grains germinated 

 on the chasmogamous stigma, each grain gave forth apparently only one 

 pollen tube. In the cleistogamous flowers, the development of the 

 pollen tube from the grain is more easily followed. Here only one tube 

 issued from each grain. The tubes pass directly down from the cleis- 

 togamous anthers to the opening of the stylar canals (Fig. 33). Through 

 these open canals the tubes pass in such numbers as to fill them. Issuing 

 from the lower end of the short stylar canals, the tubes pass in fairly 

 direct course to the ovules, where they may be seen in numbers clus- 

 tered about the micropyle. The inner integument about the micropyle 

 at this stage takes a vivid stain, suggesting the presence of some sub- 

 stance attractive to the pollen tubes. 



The history of the tubes and their nuclei in the embryo sac is the 

 same in both chasmogamous and cleistogamous flowers. As the pollen 

 tube issues from the inner end of the micropyle, it appears in two or 

 sometimes three branches (Figs. 25 and 26). Miss Riatt (39) reports 

 similar branches in Impatiens pallida, and it is recorded for other genera. 

 As these branches pass down through the embryo sac, one nucleus in 

 each branch becomes much larger (Figs. 25 and 26). This is the func- 

 tioning male nucleus. In addition to this nucleus, there appear one or 

 two smaller degenerate looking masses of nuclear material. These are 

 apparently the remains of the degenerating tube nuclei. Finally they 

 break into fragments and are lost. One branch of the tube approaches 

 the egg, and the other approaches the two polar nuclei. The polars are 

 now closely appressed, but entirely distinct. The ends of the tubes 

 swell out and rupture, and the male nuclei pass out one to the egg and 

 •one to the polars. 



