Miyake, The development of the gametophytes etc. 5 



slowly downward following the tube-nucleus which was previously 

 found in the tube (figs. 28, 30, 31). 



The stalk-nucleus now advances slightly ahead of the body- 

 cell and comes very »close to the tube-nucleus. The stalk-nucleus 

 which was at first smaller than the tube-nucleus, soon api)roaches 

 the latter in size, and as the both nuclei are of the same structure, 

 it is almost impossible to distinguish one from the other in the 

 later history of the poUen-tube (flgs. 31 — 34). As the body-cell 

 moves down the ])ollen-tube, following the stalk- and tube-nuclei, 

 it becomes more or less elongated and increases much in size; it 

 has no definite cell-wall and often assumes a more or less irregulär 

 outline (figs. 31, 32). 



The downward growth of the pollen-tube is at first relatively 

 slow and at the later stage of the development it is much ac- 

 celerated. Fig. 31 shows the stage when the pollen-tube is about 

 half way advanced the nucellar tissue in the middle of June, and 

 in fig. 32 we have the tube which has almost completed the 

 Penetration of the nucellus in the end of June. 



About the end of June, the pollen-tube reaches the female 

 prothallium and soon penetrates into the depression just above the 

 archegonial complex (figs. 70, 111). The body-cell, which is now 

 very much enlarged and almost spherical in shape, lies at the en- 

 larged tip of the pollen-tube. The tube- and stalk-nuclei are found 

 just below the body-cell, being imbedded in the granulär cytoplasm 

 with numerous starch-granules (figs. 33, 34, 106 a, 106 b). 



The body-cell has a large nucleus surrounded by the dense, 

 finely granulär cytoplasm. The nucleus has a prominent nucleolus 

 and a well marked reticulum (figs. 34, 106 a, 106 b). As the cell 

 prepares for the final division, it becomes more or less elliptical 

 in outline. The figures showing the stages of the division were 

 not found. The division takes place usually during the first few 

 days of July. Figs. 35 and 107 show the sperm-cells which are 

 completely organized. The two sperm-cells are of the same shape 

 and of equal size. Fach sperm-cell has a large nucleus and the 

 latter is surrounded by a dense mass of cytoplasm containing 

 abundant starch-granules. In the mature sperm-cell, as shown in 

 fig. 35, the starch-granules are often arranged in a dense sheath 

 immediately surrounding the nucleus and a clear area is seen in 

 the periphery of the cell. A similar arrangement of the starch in 

 the sperm-cell has been obsferved by Coker (1903, p. 11 and 

 fig. 31) in Taxodium. When the sperm-cells are fully formed, 

 fertilization takes place almost immediately. 



The development and structure of the male gametophyte of 

 Ciinninghmnia above described agree on the whole with those of 

 Taxodifim (Coker, 1903), Cryptomeria (Lawson, 1904b) and the 

 Cnpressineae (Land, 1902; Lawson, 1907; Noren, 1907). 



Formation of the Megaspore. 



The pistillate cones appear as inconspicuous buds at or near 

 the apex of shoots of the same year, in autumn. The ovules, as 



