Harper. — Cell- Division in Sporangia and Asci. 473 
sporangium-wall, as can be shown by plasmolyzing the whole 
contents of the sporangium. After this stage of greatest con- 
traction, twenty-five minutes after the full differentiation of 
the spore rudiments, swelling begins. The central ‘ lumen * 
disappears, vacuoles appear in the spore masses, and they 
become polygonal by mutual pressure but do not fuse. It 
was this swollen condition which led Biisgen to suppose that 
the spores, after separating, fused once more into a homo- 
geneous mass. Cleavage is now completed and the whole 
sporangium shrinks, due to the escape of cell-sap. The 
stages of contraction and rounding up of the spores and sub- 
sequent swelling followed by another contraction in ripening 
as described by Rothert seem T to be of general occurrence, as 
will b‘e seen from my own observations described later. 
Humphrey, in the paper already referred to, confirms most 
of Rothert’s observations as to cleavage in the sporangium. 
He also describes the cutting off of the sporangium by a basal 
transverse wall. The process of wall-formation is preceded 
by the formation of a disk of hyaloplasm which arises by the 
withdrawal of the microsomes from the originally granular 
protoplasm of the region just below the forming sporangium. 
A comparison of his description with that of Oltmanns, 
relating to the cutting off of the oogonium of Vaucheria , 
leads to the surmise that Humphrey may have mistaken a 
flattened lens-shaped vacuole for a disk of hyaloplasm. 
Pringsheim 1 first observed and figured the process of pro- 
gressive cleavage from the surface inward in the sporangia of 
Pythium entophytum . In this plant, according to the author, the 
protoplasm escapes from the sporangium before the spores are 
formed, but remains attached to the end of the sporangium 
as a spherical mass enclosed in a very delicate membrane. 
Division begins by furrows on the surface of this mass, which 
advance towards its centre and finally separate it into a mass 
of swarm-spores in a fashion very much like that described 
below for Synchitrium. As already noted, however, he takes 
1 Beitr. zur Morph, u. Phys. der Algen, ii. Die Saprolegnieen. Ges. Abhandl., 
Bd. ii, p. 63. 
