BOT.— Vol. I.] CAMPBELL— NA IAS AND ZANNICHELLIA. 



35 



appearance, having a less sharply defined contour, and they 

 are much more granular. These later stages also often show 

 more than one nucleolus, each being surrounded by a clear 

 area. Some of these nuclei have the appearance of beino- 

 formed by the fusion of two or three, but this could not be 

 determined positively (fig. 59, ^). 



The lower nucleus (fig. 59, a) finally reaches an extraor- 

 dinary size and becomes a very conspicuous feature of the 

 embryo-sac. It lies close to the wall of the embryo-sac, 

 above the antipodal cells, and is surrounded by granular 

 cytoplasm. It has a very large nucleolus, which shows a 

 distinctly vacuolar structure. The chromosomes are re- 

 markably distinct and form thick sinuous threads, staining 

 readily, and occasionally with still more deeply stained 

 granules embedded in them. The close resemblance be- 

 tween this nucleus and that of the suspensor is noteworthy. 



The development of the fruit was not followed, as Magnus 

 (1870, p. 41) has given a full account of this in his mono- 

 graph of the genus. For a time there is a growth of the 

 outer cells of the nucellus, keeping pace with the developing 

 embryo-sac; but, according to Magnus, the whole of the 

 tissue of the nucellus and inner integument is destroyed by 

 the growing embryo, and only the outer integument develops 

 further to form the somewhat complicated seed-coat. The 

 carpel itself remains membranaceous and forms simply a 

 thin investment for the seed. 



B . — Zannichellia . 



The genus Zannichellia contains but one species, Z. 

 palustris, a plant of almost world-wide distribution and not 

 uncommon in California. While several species have been 

 described, the more recent students of the genus have 

 reduced them all to a single one (Ascherson, 1889, p. 213). 

 LikevV^ms, the plant is an entirely submersed aquatic, grow- 

 ing either in stagnant or running water. While usually a 

 fresh-water plant, it is also said to grow in brackish water. 

 In general appearance the plant recalls Naias, but has longer 



