WITH NOTES ON OTHER SPECIES. 95 



SO, then the only real differences between these two organs are found in the concen- 

 tration of the protoplasmic contents of the latter into one or several separate masses 

 and the fusion of the nuclei of these masses into one, to be restored by subsequent 

 division. These differences are of purely phj^siological and sexual significance and 

 are inheritances from the truly sexual ancestors of these plants. But on the other 

 hand, it is evident that sporangia, chlamydospores, and ojgonia are strictly homolo- 

 gous organs. 



It is easy to speculate upon the relationships of the present familj^ to various 

 other groups of Algoe and Phy corny cetes ; but this would be of little profit. Until 

 our knowledge of some details of the development of the plants concerned, especially 

 of their cytology, is more complete, it seems well to refrain from further conjecture. 



Occurrence and Distribution. 



The Saprolegniacem are found more or less commonly in all fresh waters, but 

 prefer such as are pure and clear. They occur most abundantly and develop most 

 luxuriantly in such waters as contain and favor the growth of the pure-water Algae, 

 ConjiigatcB and CMorophyceoR. In stagnant waters or those which are polluted by 

 organic matter, they may be found, but their development is usually slow and 

 feeble, and is often quite arrested by the swarms of Bacteria and Infusoria which find 

 their congenial conditions in such places. The most striking exception to this 

 general statement is afforded by Leptomitus lacteus, which grows especially in 

 waters containing considerable organic impurity ; and the same is perhaps true of the 

 other Leptoyniteae. 



These plants are usually saprophytic and grow upon animal and vegetable 

 remains. The latter may include dead, woody or herbaceous parts of vascular plants 

 or even decaying Algae. On the last I have found L. lacteus growing vigorously. 

 But it is on animal remains that they flourish best; and of these the most favorable 

 appear to be insect bodies. The reason for this fact probably lies in the circumstance 

 that these bodies, being pi-otected by a chitinous skeleton, are not so exposed to the 

 attacks of putrefactive Bacteria, and therefore decompose slowly and cause little 

 pollution of the surrounding water, as compared with a bit of naked flesh of the same 

 bulk. The SajJrolegniacece, too, undoubtedly act as scavengers in appropriating for 

 their own growth the more readil}'^ available organic compounds of the dead body. 

 In cultures in a small voluritie of watei", the evidences of decay disappear after a few 

 days, coincidently with, or even before the cessation of active growth in the fungus, 

 consequent upon the exhaustion of available nourishment. 



A. p. S. — VOL. XVII. M. 



