LIFE HISTORY OF PINUS 7 



the tube remained closed until after the formation of the pro- 

 embryo, when it was ruptured by mechanical means. The 

 great abundance of starch in the pollen-tube of the Abietinece 

 was also mentioned at this time. While the " Higher Crypto- 

 gamia " appearing in 1862 was largely a translation of Hof- 

 meister's earlier publications, it likewise presented many new 

 observations. The fact was noted that in Pinus the integument 

 surrounds the nucellus, leaving open above its apex a wide 

 micropylar canal. In all the Conifer a > after the embryo-sac 

 was entirely filled with cellular tissue, certain cells near the 

 micropylar end ceased dividing but increased markedly in size ; 

 the other cells of the endosperm continued to multiply in num- 

 ber, but remained comparatively small ; thus the corpuscula 

 were differentiated. After the cutting off of the neck-cells in 

 the Abietinece , additional cells were developed at the top of the 

 endosperm, giving rise to the depressions referred to in 1851. 

 Scarcely a day intervened between the approach of the pollen- 

 tube and the formation of a four-celled pro-embryo at the base 

 of the corpusculum, and this occurred contemporaneously in all 

 ovules of all trees growing under similar circumstances. 



The works of Strasburger on this subject have been more 

 numerous and complete than those of any other investigator. It 

 is extremely interesting to note how his interpretations have kept 

 pace with the improvements in methods of research. In 1869 

 he traced the development of the endosperm from the free cells 

 lining the embryo-sac to its maturity, and established the fact 

 that shortly before fertilization the central cell divides to form 

 the canal-cell and the egg-cell. He confirmed Hofmeister's 

 observations regarding the channels in the upper part of the 

 endosperm, and the presence of a closed pit at the apex of the 

 pollen-tube ; but he did not observe the nuclei in the pollen-tube, 

 and remarked that, inasmuch as the sexual organs touch "in 

 these plants, spermatozoids would be superfluous and were, in 

 reality, not present. He added, however, that their place was 

 taken by granular protoplasm and starch grains which exercised 

 the same fertilizing effect on the egg as do spermatozoids. 

 After fertilization four nuclei were detected at the base of the 

 corpusculum and a division into a cross took place, these cells 



