94 DuGGAR : Development of the Pollen Grain 



r 



■ 



eral instances In which the third cell retained Its normal appearance . 

 later than the first two ; but ultimately the fourth cell develops the 

 embryo-sac. 



In having a single axial row of four cells, and In possessing no 

 tapetum, Bignonia agrees with such monocotyledons as Sisyrin- 

 cJihim iridifolium and Ilcmcrocallis fniva (usuall)-), according to 

 Strasburger * ; and among gamnpetalous dicotyledons, so far as I 

 have found from literature accessible, with all that have been studied, 

 namely, with Composltae * and Labiatae * ; also with some Ranun- 



t 



+ 



Einbiyo-sac 



The embryo-sac develops by the Immediate growth of the 

 fourth or lowest macrospore in the axial row, as mentioned. Since 

 reduction has already taken place, its nuclear divisions are of less 

 interest. The embryo-sac Is late In developing, and it is not ma- 

 ture when the flower is fully open. As a rule, it seems to become 

 unhealthy In this conservatory material after the first or second di- 

 vision. The nuclei are small, and divide rapidly. Generally, the 

 embryo-sac became disorganized so readily, and latest ages were so 

 difficult to secure, that lack of effcctivc pollination was suggested as 

 apossible cause of the difficulty. Artificial pollination with pollen 

 from the same plant was Ineffective, and attempts were futile to secure 

 In good condition pollen from other plants in distant greenhouses. 

 Embryo-sacs with two and with four nuclei were more conmionly 

 seen, as m Fig. i8 ; but only in a single Instance was a mature 

 embryo-sac found, and this was perfectly normal, with the char- 

 acteristic eight nuclei, as shown in Fig. 19. The three antipodals 

 are free, with no indications of disintegration, the polar nuclei are 

 beginning to fuse, and the sexual nucleus has taken up its position 

 Immediately below the two synergids. 



* Strasburger, E. Angiospermem unci Gymnospernif n. 



\a. JIann, L. E. The Eml)ryo-sac of Myosurm minimus. Trans, and Proc of 

 Bot. Soc. EdmburgL, 29: 351. 1S92. b, Mottior, D. M. Coutribuliuas to the Era- 

 brology of the Ranunnilaceae. Bot. Gaz. 20 : 241, 296. 1895. 



JAncTrcus, F. M. Development of tlie "e^rnhx^o-^^c o^ Masonia diphylla. Bot. 

 Gaz. 20 : 423. 1895. 



