68 



plied, or even of developing until its protoplasm is exhausted, without further nour- 

 ishment. 



Scattered through the protoplasm without order, but commonest at the nodes 

 of the granular network, are the nuclei, normally ellipsoidal in form, and each with a 

 distinct central mass which stains more deeply than the rest of the nucleus (Fig. 4). 

 These central masses have been generally termed nucleoli, but they seem clearly to 

 correspond rather with the chromatin bodies of more highly organized nuclei, and 

 will, therefore, be better designated as chromatin-masses. Between the chromatin- 

 mass and the nuclear membrane is a considerable space occupied by a substance 

 which stains very slightly with hsematoxylin. The nuclei are most abundant in the 

 young parts of the hypha, where the protoplasm is densest. They increase in num- 

 ber, with the apical growth of the thread, by fission. The division of the nucleus is 

 preceded by the division of the chromatin-mass, and commonly occurs in a plane at 

 right angles to its long axis (Fig. 5). I have observed some cases, like one shown 

 in Fig. 4, where two nuclei lie close together, with their long axes parallel, bat have 

 never seen preliminary stages to convince me that they have resulted from the 

 division of a nucleus in the plane of its long axis. Hartog states ('89) that he has 

 observed karyokinetic phenomena in some cases, but I have been unable to find 

 evidence of any other than direct division. 



The growth of the hyphse takes place at their blunt or somewhat pointed tips. 

 Data as to the rate of growth are very few. Pringsheim ('51) reports a rate of 

 400,y. {= .4 mm.) per hour in a new filament of Saiwolegnia, growing into an emptied 

 sporangium. Hine ('78) records having observed a growth of 70 to 90,a per hour 

 during three hours' observation of a filament of Saprolegnia ; and I have measured a 

 growth of about 100,a per hour in a vigorous hypha of AjjJianomyces, while the germ- 

 tube from a zoospore of the same species grew at the rate of about 40;/ per hour in 

 water. 



The purely vegetative branching of the hyphre is sometimes dichotomoiis at the 

 principal divisions of the larger ones, but commonly of the monopodial type in the 

 small branches. In most species the branches may arise from any point and develop 

 by apical growth at acute or right angles with the main axis. In the genus Leptomitus, 

 as here limited, branches arise only from the acroscopic ends of the segments, close 

 to the origins of the next segments of the axial series (Fig. 6). They are separated 

 by constrictions from their parent segments ; but when the segment next below a 

 sporangium gives rise to a branch, it grows out for a short distance without con- 

 striction, and then produces a new segment (Fig. 116), as Pringsheim has pointed 

 out ('60). 



