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: i. 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 of the Phycomyoetes 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 J , 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 2 

 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. 

 " Sitzsber. d. Niederrhein. Ges. Aug. 4, 1879. 



