i 909 ] YA MA NO U CHI— MI TO SIS IN FUCUS 175 



development. The following brief account of the essentials is 

 illustrated by figures from the apical portions of male and female 

 plants. Since the mitoses in male and female plants are precisely 

 alike, the following account may be understood as applicable in 

 either case. 



The nuclei in the growing apex of the plant are somewhat larger 

 than those in older regions of the thallus, sometimes filling almost 

 all of the lower half of a narrow elongated palisade cell, such as 

 constitutes the surface layer of the thallus. The cells are filled with 

 an abundance of contents, such as plastids, physodes, and other 

 granular substances of undetermined nature. In regions where such 

 contents are scarce, the cytoplasm shows a very fine alveolar structure, 

 which gradually becomes granular, even, and homogeneous toward 

 the nuclear membrane. 



In early prophase the chromatin network of the resting nucleus 

 changes to a structure in which numerous chromatin knots become 

 more and more pronounced, until they become transformed into 

 well-developed chromosomes (figs, ia, ib, 7). The chromosomes, 

 which at first appear very irregular in size and shape, now become 

 quite similar in form, slightly bent, and in this condition they are 

 ^ranged in an equatorial plate (figs. 2, 8). 



During the chromosome development within the nucleus, the 



the two poles. 



transformed 



somes 



asmic 



appear first in the late prophase, when the chromosomes are 

 Ranged in the equator (fig. 2). The nuclear membrane persists 

 generally up to late metaphase, being especially well marked toward 

 lie 6 e , qUat0rial re § ion - J n the polar region where the centrosomes 

 le > the membrane will perhaps be very faint, so as to allow the 



doping spindle fibers to _ . _ _ . . ' * 



1 ra P. are formed outside. Owing to the minuteness 



intrude 



teA " 1S ramer dlrtlc ult to make 

 *°* origin of the centrosome and 



divisions 



segmentations 



is mor 6 nUmber of cnr omosomes in the early prophase (figs, ia, ib) 

 ° re than 6o > but 64 chromosomes can be counted with certainty 



