74 DIVISION I.—-GENERAL MORPHOLOGY, 
Peronosporeae; more rarely they are intercalary. Their spores are produced by 
division without formation of parting walls and conform to two chief types: 1. A 
parietal layer of protoplasm at least is not included in the division and is left behind 
in the sporangium, as is the case in asci. 2. No parietal layer remains behind, as in 
the sporangia of the Phycomycetes, which show much variation in details. 
a. In the sporangia ofthe Phycomycetes the whole of the protoplasm, whether 
parietal and enclosing a vacuole or filling the lumen of the cell, is divided to form the 
spores. The number of spores directly produced by the division is not fixed in any 
species except perhaps in Tetrachytrium‘, and is often very large, as in Mucor, Pilobolus 
and large Saprolegnieae. The division usually appears to be simultaneous ; but Biisgen 
observed under very favourable circumstances in Leptomitus lacteus and Mucor that 
the protoplasm was divided by very rapid bipartitions into successively smaller portions 
up to the final formation of spores. When the division is complete the future limiting 
surfaces of the spores are at first indicated by granular plates, but these are at once 
replaced by homogeneous delicate and narrow partition-layers, which often however 
become broader; these layers proceed probably from the blending of the grains and 
usually continue of a soft gelatinous consistence, being directly transformed into plates of 
cellulose only perhaps in species of Dictyuchus. In the Mucorini and in Dictyuchus 
clavatus the spores which lie between such dividing layers become invested at once 
with a firm cellulose membrane; in other species a distinct membrane does not appear 
before the spore leaves the sporangium. The early stages of the division in 
Aphanomyces show exceptional deviations from the ordinary type. No growth of 
the spore when it has once been separated off takes place inside the sporangium in 
any of the above cases. 
The process of division may be observed in its greatest completeness in the 
sporangia of the larger Saprolegnieae which live in the water; in Saprolegnia, 
for example, Achlya and Leptomitus lacteus. The sporangium is a large club-shaped 
cell delimited by a transverse wall from the unicellular tubular sporangiophore. It 
is densely filled with a coarsely granular protoplasm, or may have a large axile 
vacuole. Shortly before the division the protoplasm becomes everywhere uniformly 
and finely granular and has small inconstant vacuoles at wide distances from each 
other. It is then suddenly divided by granular plates, which look like rows of granules 
when seen in profile, into numerous polyhedral or polygonal portions, the future spores, 
which in Leptomitus, as was said above, are formed by rapid successive bipartitions. 
The partition soon becomes more pronounced, the partition-streaks which were before 
granular now become homogeneous, and no longer appear as fine clear lines but 
grow broader as the spores are rounded off. With this the separation of the spores 
is complete in the cases which we are considering: the substance of the partition-plate 
which is derived apparently from the granules that were previously present continues 
homogeneous, soft and capable of swelling. Colouring reagents, as Fr. Schmitz? 
first discovered, show the presence of a number of nuclei in the sporangium as 
soon as it is delimited, and a division of them afterwards. Each spore obtains a 
nucleus, which has been directly observed to proceed in Leptomitus from the 
division of the original nuclei. These processes which lead at once to the for- 
mation of spores are however preceded by other separations in which the behaviour 
of the nuclei has not been clearly ascertained. The coarsely granular protoplasm 

1 Sorokin in Bot. Ztg. See also below, section LII. 
2 Sitzsber. d. Niederrhein. Ges. Aug. 4, 1879. 
