The nuclei in the yeast cells and mycelium of Blaston~yces dermatitidis were studicd in the living statc and in hxed preparations stained by various techniques. Yeast cells and mycelium are ~nultinucleate. Interdivisional and recently divided nuclei migrate into the yeast buds. Nuclear migration also occurs from one cell to another via the pores in the septa of elongated yeast cells and mycelium. Interdivisional nuclei in yeast cells and mycelium are composed of a spherical Feulgen-negative central body enveloped by grdnuldr Feulgen-positive chromatin. A nuclear membrane has not been observed surrou~tdir~g living or stained nuclei either in yeast cells or mycelium. During nuclear division. the chromatin condenses, then elongates, and finally pulls apart to form taro slster rluclei. The role played by the central body during nuclear division is obscure. However, it was noted that during the division of the chromatin the central body did not divide but became progressively smaller and apparently disintegrated in the cytoplasm. New central bodies are formed in recently divided nuclei. Mitotic figures such as a spindleor a metaphase plate have not been observed in any libing or stained prep,iratlons. Complexes of chromosome-like elements were noted in some hyphae, possibly those associated with conidial-bearing stallts. Counts made of such "chromosomes" in several of these complexes revealed a minimum number of six and a maximum of eight.' Manuscript

No abstract

The nuclei in the vegetative hyphae of Schizophyllum commune do not divide in a manner directly comparable to ordinary mitosis. During division the tightly packed chromatinic granules become loosely arranged following which they contract into a densely stained bar. As division proceeds this bar of chromatin elongates and then constricts at its mid-region. At the end of division the extremities pull apart quickly to form the chromatin portions of the two sister nuclei. The Feulgen-negative central bodies decrease in size and at the end of division their remnants lie free in the cytoplasm. New central bodies arise in the maturing sister nuclei. Throughout division metaphase plates, spindles, or individual chromosomes were not observed in any of the stained or living preparations. A nuclear membrane has not been observed surrounding any of these nuclei.

BAKERSPIGEL, ALF:XANDEil. (New Mount Sinai Hospital, Toronto, Canada.) The structure and manner of division of the nuclei in the vegetative mycelium of Neurospora crassa.-A;;;-~~:-Jour. Bot. 46131: 180-190. ITJ;;:s. 1959.-A&~c~iption has been--gi~en of the stnl~ture and-;;lanner of division of the nuclei in the conidia and vegetative mycelium of the ascomycete, Neurospora crassa. This is another example of a fungus in which the vegetative nuclei do not appear to divide in the manner of classical mitosis. Instead, as division proceeds, the chromatin forms complexes of chromosomal filaments which then contract. At the end of division the contracted chromatin constricts and pulls rapidly apart without the aid of a visible spindle. Individually recognizable chromosomes were not observed to align themselves on a metaphase plate. In the vegetative mycelium of N. crassa the central body elongates and divides by constriction at the mid region. Thus at the end of division each of the sister nuclei is composed of a portion of the original chromatin and central body. It is suggested that both the elongating central body and the densely stained granule in the chromatin of these nuclei play significant roles during nuclear division. 188 A;\IERI CAN JO UR NAL OF BOTA NY [ Vol. -16 c f l 75 o . J Fig. 75-76. Semidiagramrnatic representation of nuclear division in the vegetative hyphae of N . crassa.-Fig. 75. ( He l· Giemsa technique.) a. An interdivisional nu cleus. b, c. Early division. d-m. Later divisional figures. Not e the double granules in 1, m. n, o. End of division. p, q. Post division, showing 2 sist er nuclei following their separation. Refer to text for description of individual sequences.-Fig. 76. Semi dia grammatic repr esentation of nucl ear divi sion in living vegetative hyphae of N. crassa. a-c. Vari ousl y shaped interdi visional nuclei. d. e. Early divi sional stages. f-h. Later di visional stages. i. End of divi sion . j , k. Post di vision . Th e central bodi es a re evid ent in th e sister nucl ei shown in k. 1. Ma turing sister nucl ei. Duration of di vision : a-f, approximately 6 min. , I-], 2-3 min ., j-I, approximat ely 1 min.Refer to text for description of di visional sequences.