284 Journal of Agricultural Research voi. iv, no. 4 



by the protoplasmic stream to the developing presporangium in which 

 no divisions occur. The number of nuclei assembled before the organ 

 is segmented off by a cross wall varies greatly. Presporangia containing 

 as few as 4 were seen, while 200 or more were not uncommon. In the 

 one illustrated 162 are shown (Pi. XLIV, fig. 7). The nucleus at this 

 stage is spherical to oval and contains typically a single nucleolus located 

 at one side, frequently protruding slightly from the body of the nucleus 

 (PI. XLVI, fig. I, 8). In some cases, especially in the zoospore, the 

 nucleus may contain two or even three nucleoli. The mitochondria, 

 which are numerous in the vegetative hyphae (PI. XLVI, fig. 8), where, 

 in certain stages at least, they are arranged so as to suggest a peripheral 

 distribution, are still more abundant in the presporangia (PI. XLVI, 

 fig. i), where they are evenly distributed throughout in great numbers. 

 Following the development of a division wall to cut off the presporangium, 

 numerous vacuoles develop within that body (PI. XLVIII, fig. i). These 

 coalesce (PI. XLIV, fig. 13) as they increase in size and develop the pres- 

 sure which results in the rupture of the inclosing wall (PI. XLIV, fig. 

 6, 10). Plate XLIV, figure 6, shows the condition just at the instant 

 following rupture. The thin wall of the sporangium is seen covering 

 the protruding cytoplasm, which is just beginning to escape. The 

 sudden relief of tension is shown in a striking manner by the influence 

 temporarily exerted on the form of the nuclei at the narrower portion 

 of the body. Plate XLIV, figure 10, represents the process at a later 

 stage. Here the rupture took place at the tip of one of the branches. 

 At two places within the wall of the presporangium the membranous 

 wall of the sporangium is seen receding al/ong the cavity, while the flexi- 

 bility of its structure may be judged from the spherical shape of the 

 delivered portion. 



Sections of the young zoosporangium show at first an entirely undiffer- 

 entiated condition to be followed by the development of vacuoles and 

 the migration of nuclei toward the periphery (PI. XLV, fig. 5). The 

 vacuoles coalesce, developing so as to form a relatively large irregular 

 central cavity from which cleavage lines split outward. Meantime the 

 nuclei arrange themselves at a uniform distance from the outer surface 

 with their nucleoli turned toward the center of the mass (PI. XLV, fig. i). 

 Cleavage furrows soon become apparent on the periphery so as to de- 

 lineate the outlines of the future spores (PI. XLV, fig. 4). Reference 

 has already been made to the first appearance of these furrows on the 

 exterior in living material. A single large vacuole develops near each 

 of the nuclei (PI. XLV, fig. 2, 4) and cilia appear in the indented areas 

 between the future spores (PI. XLIV, fig. 3). In this way a single row 

 of zoospores is cut out at the periphery of the sporangium (PI. XLV, 

 fig. 2). 



Cleavage usually progresses somewhat more rapidly in one side of the 

 sporangium than in the other. It sometimes happens that the first 



