HISTORICAL SKETCH 



11 



They further found that one of these nuclei originally lies in a 

 small cell cut off at the periphery of the pollen grain but later be- 

 comes free by a dissolution of the partition wall. Elfving also 

 germinated pollen grains in artificial media, and when this was un- 

 successful, he made preparations of pollen tubes from dissected 

 styles. Here he was able to find the three nuclei which we now know 

 to be the two male gametes and the tube or vegetative nucleus. 

 Unfortunately both Strasburger _________ 



and Elfving made the mistake 

 of interpreting the smaller cell 

 in the pollen grain as vegeta- 

 tive or prothallial and the larger 

 as generative. They further 

 thought that all the nuclei in 

 the pollen tube dissolved and 

 disappeared before fertilization. 

 These mistakes were, however, 

 rectified by Strasburger in a sub- 

 sequent paper (1884), which will 

 be referred to later. 



For our knowledge of the or- 

 ganization of the embryo sac we 

 are indebted in the first instance 

 to the works of Hofmeister 

 (1847-1861). Working wholly 

 with cleared preparations and 

 freehand sections, he succeeded 

 in identifying the two groups of 

 cells at the opposite poles of the embryo sac. Those lying at the 

 micropylar end were designated as the "germinal" or "embryonal" 

 vesicles, all capable of giving rise to embryos and therefore to be 

 regarded as homologous with the corpuscula (archegonia) of the 

 gymnosperms. The cells at the chalazal end were considered to be 

 prothallial, and the embryo sac itself was interpreted as homologous 

 with the megaspore or female gametophyte of the heterosporous 

 pteridophytes and the gymnosperms. 



Although Hofmeister's work was important, he failed to dis- 

 tinguish clearly between the synergids and the egg and regarded all 

 three of them as having the same function. Further, he was unable 

 to trace the mode of origin of the embryo sac, the general opinion 



Fig. 9. Edward Strasburger. (Photo- 

 graph obtained through the courtesy of 

 Prof. A. W. Haupt.) 



