2 THE SAPROLEGNIACEAE 



and leads only to a slight rocking or jerking motion. Again, the spores 

 move as a mass and not individually. As the first spores escape the 

 others draw away evenly from the cell wall until as the emptying proceeds 

 the spores form an axial column which remains solid and moves toward 

 the opening, the spores having their long axes all parallel to the long 

 axis of the sporangium. The spores on the bottom of the column can be 

 plainly seen in places where they are slightly separated and it is per- 

 fectly obvious that if any ciliary action is going on at all it is negligible 

 as a motive force. Absolutely conclusive are the cases where large 

 masses of protoplasm are ejected from a sporangium in undifferentiated 

 form, the entire contents at times plastically pouring out of the small 

 mouth (see page 9). A similar case is the ejection of the bladders from 

 the sporangia of Pythium, Rhipidium and Araiospora. In Aphanomyces 

 the main bodies of the elongated spores becomes separated by an ob- 

 vious interval soon after the sporangium opens (they are actually connected 

 by a slender strand of protoplasm), and if one gets caught in the open- 

 ing all the others in the row stop suddenly and start forward again only 

 when the obstruction is removed, showing that the spores are being pass- 

 ively carried forward by the surrounding medium. In Leptolegnia the 

 spores emerge with force but do not swim actively away as would be 

 expected if this force were continued. They slowly move about at the 

 sporangium mouth reshaping themselves along another axis preparatory 

 to active swimming. It often happens in Achlya that one or more groups 

 of spores on emerging become separated from the main mass by some 

 distance (as several times the diameter of the spores). If one of these 

 masses is touched all the groups are moved or jerked by the impulse. This 

 shows a connecting medium less fluid than water, and this medium we 

 now know to be delicate strands of protoplasm (see page 4). 



Just what causes the internal pressure that drives out the spores has 

 not been known with certainty. There is a shrinkage in the size of the 

 sporangium during the discharge, but this could account for only a small 

 part of the result. A sporangium of Achlya racemosa measured by us 

 was 2iii thick before and 18.71J1. thick after the discharge. Aside from 

 this there would seem to be only two possible alternatives, the simple 

 absorption of water due to higher osmotic tension within, or the swelling 

 of a gelatinous medium by absorption of water. All the phenomena 

 could be explained by the assumption that the expulsion is due to the 

 swelling of a peripheral substance inside the sporangium, and that this 

 is the cause was the opinion of deBary, as clearly expressed in his Com- 

 parative Morphology of the Fungi, etc., p. 82. The only difficulty in the 

 way of the acceptance of the assumption that a swelling mucus is the 

 cause of expulsion is the entire failure so far of all efforts to demonstrate 



