44 THE SAPROLEGXIACEAE 



10. Growth with sporangia, then gemmae; or growth with oogonia, then gemmae; or 

 growth with sporangia and oogonia and then gemmae: — -in the items 3, 5 and 6 above, 

 when the culture is continued to the complete exhaustion of the nutrient material. 



General conclusions in regard to conditions for the formation of 

 oogonia and anthcridia are summarized as follows (1. c, p. 566): 



1. In a mycelium which is constantly given fresh nourishment no oogonia are ever formed. 



Young, just formed oogonia were, by means ol fresh, soluble food, induced to vege- 

 tative growth. The old were, however, killed. 



2. If a strongly nourished mycelium is changed to a medium of low nutritive value (in 



which the formation of sporangia is rare or absent) oogonia are formed in a few days. 



3. In a good soluble food, preferably at such concentration that the sporangia cannot 



be formed, the mycelium begins to form oogonia as soon as the solution is chemically 

 changed on account of its growth, and has lost its nutritive value. 



4. The formation of oogonia is particularly encouraged through phosphate, which is 



likewise necessary to the formation of the antheridia. In a soluble food that is 

 poor in phosphate oogonia are formed, but no antheridia; particularly abundant are 

 such oogonia in a pure solution of haemoglobin. 



5. In many soluble foods, for example in peptone, gelatine, etc., are excreted certain prod- 



ucts of assimilation of the mycelium which hinder the formation of oogonia. 



All of the following cultures were made by us from a single 

 spore culture of No. 10 of January 15, 1913: 



In equal parts of 5% maltose and .01% peptone. The solution was inoculated with 

 swimming spores on February 14, 1913. By the l8th or igth the culture had covered 

 the petri dish, and had formed a large number of oogonia with perfect eggs. Oogonia 

 were somewhat inflated with eggs not filling the cavity; eggs of usual number, vary- 

 ing in size from 15.5-27.7fj., averaging about 24.4(x. This is smaller on average than 

 other cultures. Of scores of oogonia examined only one or two had antheridial 

 branches attached, and no antheridia were cut off. No sporangia were formed, and 

 therefore all oogonia were spherical. This is the only Saprolegnia that forms normal 

 oogonia and eggs in this medium. 

 On ant in rain water. Sporangia abundant. Oogonia plentiful, heavily pitted, nearly all 

 spherical, and containing 1-6 eggs, most with 2 or 4 eggs. Many oogonia do not 

 perfect the eggs. Scattering gemmae. Repeated this experiment with same results 

 except that there were more cylindrical oogonia. Almost no antheridia. It is 

 evident that the purer the water the fewer the antheridia. 

 On ant in spring water. Abundant sporangia. Oogonia very abundant, nearly all 

 spherical, a few cylindrical; pits abundant: oogonia very healthy, all maturing the 

 eggs, which vary from 1-12, mostly 1-6. Antheridia on probably 33% of the 

 oogonia. Very few gemmae. Repeated this experiment with same results, except that 

 there were more cylindrical oogonia. 

 On ant in distilled water. Growth shorter and stouter than in the two preceding cultures. 

 Sporangia abundant and stout. Oogonia very abundant and large, with thick, heavily 

 pitted walls, spherical or cylindrical, the proportion of cylindrical ones being much 

 larger than usual, comprising about yi of all, very healthy and maturing all eggs, 

 cylindrical ones generally with 4 eggs, often with 2 or 3, spherical ones sometimes with 

 12 eggs, but generally from 1-8. The eggs of this culture average larger than in mal- 

 tose-peptone, varying from 14.8-33.3iJ., averaging about 25.8tJ.. The few eggs that 

 reach the largest size are only one to the oogonium. The smallest size may occur in an 



