Schwarze: Cleavage in Sporangia 145 



Zelle ab, schwillt zur Kugel an, in deren Hohlraum sich die Quer- 

 wand meist mehr oder weniger einstiilpt und die sog. Columella 

 bildet." In so recent a textbook as Densmore's General Botany 

 (17) we find: "This sporangial cell now expands with great 

 rapidity and with its expansion the wall separating it from its 

 hyphal stalk grows in surface area and assumes a convex form, 

 protruding into the growing sporangium until it comes to occupy 

 fully one half or two thirds of the sporangial cavity, when it is 

 called the columella/' Densmore also figures (fig. 141) the colu- 

 mella as at first a plane wall, which is later arched up into the 

 sporangium. 



The method of spore formation in sporangia was studied, with 

 interesting results, as early as 1859, following the discovery of cell 

 formation by division, as worked out by Von Mohl and others, and 

 has been prosecuted up to the present day. While the pioneers 

 were influenced and sometimes misled by theories relative to cell 

 formation in general, the fact remains that as early as 1859 Prings- 

 heim (44) observed and figured progressive cleavage from the sur- 

 face inward, essentially as we know the process today, in the 

 sporangia of Lagenidium entophytum (Pringsheim) , Zopf (Pyth- 

 ium entophytum Pringsheim). He writes as follows: "Erst vor 

 der Oeffnung des Sporangium beginnt nun in dem ausgetretenen, 

 zur Kugel zusammen gebalten Inhalt, eine an der Peripherie be- 

 ginnende und nach dem Centrum vorschreitende Sonderung durch 

 welche die Protoplasmakugel schliesslich in eine grossere Anzahl 

 von Schwarmsporen zerfallt [PI. 8, fig. ib]" 



General conclusions relative to spore formation in sporangia 

 found in some recent papers are quite at variance with observations 

 which seem well established by earlier students. One must infer 

 that some of the recent writers must have overlooked Rothert's 

 (46) paper entitled, " Die Entwicklung der Sporangien bei den 

 Saprolegnieen." 



The general history of this literature has been treated by Swingle 

 (50) and recently by Moreau (37) and Harper (25). I shall 

 refer only to points bearing on matters that seem still unsettled, 

 especially the question as to the occurrence of so-called simulta- 

 neous cell-division. 



