Dec. 23. i9i8 Parasitism of Cronartium ribicola 641 



its full size the fusion nucleus, formed by the union of the two nuclei in 

 the young teliospore, migrates from the teliospore into the promycelium 

 and starts to divide (Pi. 57, E). The membrane becomes irregular and 

 disappears (PI. 57, F) at the same time that the chromatin granules increase 

 in size. These granules become longer and more deeply-staining units, 

 which form a tangled mass in the position occupied by the fusion nucleus 

 when it moved out into the promycelium (Pi. 57, G). A definite spindle, 

 with centrosomes at the poles, then develops. At the middle of the 

 spindle the chromatin tangle becomes arranged in an equivalent of the 

 equatorial plate stage. In the next stages the chromatin is in the form 

 of separate units (PI. 57, H, I), which can be clearly seen under favorable 

 conditions and proper differentiation. Plate 57, I, shows 16 such units 

 which apparently are equivalent to distinct chromosomes. They sepa- 

 rate into two groups, and the elements of the groups migrate along the 

 spindle to the corresponding poles (PI. 57, J, K). Radiations from the 

 region of the centrosomes are present, but not easily stained during 

 metaphase (PI. 57, I), and quite long and prominent throughout ana- 

 phase (Pi. 57, K) and at telophase (PI. 57, L, M). They seem to be due 

 to cytoplasmic condensation rather than of the nature of true astral 

 rays. The two chromatin groups in late anaphase are condensed into 

 irregularly lobed masses (Pi. 57, L, M) at the ends of a more or less 

 curved strand of suspension fibers, recalling Blackman's figure 31, 

 Plate 21, (2). The suspension fibers disappear, the daughter nuclei 

 reorganize around the chromatin groups as centers, and a wall divides 

 the young promycelium into two cells (Pi. 57, N). A second division 

 follows immediately (Pi. 57, O, P, Q). The two pairs of granddaughter 

 nuclei thus formed are then separated by cross walls (Pi. 57, R), and the 

 4-celled promycelium completed. As a rule, the empty basal portion of 

 the promycelium is also cut off by a wall, so that the promycelium really 

 has five cells, four active and one, the stalk, practically dead. Each 

 nucleus is relatively small, with a definite nucleolus and a minute centro- 

 some. The contents take the form of a fine granular network. 



From each of the four active cells of the promycelium a stout sterigma 

 is protruded (PI. 57, S), on which a single spherical sporidium is formed 

 (PI. 57, V). The nucleus of the cell migrates through the sterigma 

 (PI. 57, U), taking on an irregular shape during the process, and then 

 rounds up into its normal form (Pi. 57, AA). The division of this nucleus 

 to form a binucleate sporidium (PI. 57, GG) is quite common, and the 

 karyokinetic figures are particularly striking. Early and late anaphase 

 stages are represented in figures EE and FF, Plate 57. The nuclear 

 behavior in the formation of secondary sporidia was not followed. In 

 germinating sporidia the nucleus probably migrates into the germ tube 

 and there divides, although the figures of this process were indefinite 

 and unsatisfactory. Figure BB of Plate 57 illustrates a common con- 

 dition which indicates that the nucleus is preparing to divide, at the same 



