Charles J. Chamberlain 



reappear, but are not centered in any single point. When the nuclear membrane 

 begins to form, the radiations again become indistinct and disappear as before. Just 

 before the spindle reaches its full length (Fig. 6), the radiations often attain their 

 greatest prominence, sometimes appearing as extremely coarse strands. In nearly 

 all cases, even in very thin sections, some of the rays can be traced from the pole of 

 the spindle to the Hautschicht. The diameter of the rays is usyially greater at the 

 polar end, but a slight increase in diameter at the Hautschicht also is not uncommon. 

 The rays are usually simple, but may be branched especially during the earlier stages. 

 It is worthy of note that the radiations are most pronounced and stain most deeply 

 with gentian violet, while the nucleus is elongating and its poles are separating from 

 each other ; and, further, that during this period many of the radiations connect the 

 poles with the Hautschicht. The explanation which we venture to suggest is that the 

 radiations take an active part in separating the poles from each other. The fact that 

 the radiations disappear as soon as the poles have reached their widest separation 

 supports this hypothesis. The reappearance of the rays in the telophase does not 

 seem to be so definitely concerned with movement, because they again disappear before 

 the nucleus has perceptibly changed its position: still, it is possible that there may be 

 a slight movement of the nucleus toward the center of the new cell. The reappear- 

 ance, however, takes place as the nuclear membrane begins to be formed, and it may 

 be an expression of kinoplasmic activity during the formation of a Hautschicht sur- 

 rounding the nuclear membrane, or the rays may be contributing to the formation of 

 the nuclear membrane itself, which, we believe, is largely kinoplasmic in its nature. 



THE SECOND MITOSIS IN THE GERMINATING SPORE, WITH REMARKS ON APICAL CELL, 

 ANTHERIDIA, NUCLEOLI, AND CHROMOSOMES 



The second mitosis is remarkably easy to fix and stain; so that, while the first 

 mitosis, if equally well prepared, might show the early prophases with a little more 

 clearness, our material aft'orded a better study of these stages during the second mitosis. 



In studying the second mitosis, special attention was devoted to the centrosphere 

 and to the origin of the achromatic structures. The terms "centrosome" and "cen- 

 trosphere" are frequently confused. Until much more is known about the origin of 

 these structures and their relation to each other, it is hardly worth while to attempt 

 any definitions. A typical centrosphere — as the term is used in this paper — is shown 

 in Fig. 12 (Plate XXVI). The centrosphere consists of the same substance as the astral 

 rays and the spindle fibers. The elongated body toward which the rays converge in Fig. 

 15 is also a centrosphere, and the densely staining masses at the poles of the spindle in 

 Fig. 6, although not organized into a definite body, consist of the same material as cen- 

 trospheres and, at an earlier stage in mitosis, may have had a more definite form. We 

 have not intended to represent a centrosome in any of our figures. Bodies which have 

 the superficial aspect of centrosomes are shown in Figs. 14, 16, and 17, but here the 

 sharply staining body at the center of the centrosphere is, without doubt, the cut end 



333 



