746 



SCIENCE 



[N. S. Vol. XXXIII. No. 854 



more successful in producing these bodies than 

 previously, due in part to the use of the lima 

 bean medium in a modified form, and while 

 these bodies showed a still greater modifica- 

 tion toward the oogonial type, they did not 

 succeed in producing in their cultures any 

 bodies of the nature of antheridia. 



During the past year the writer, with the 

 aid of his assistant, Mr. E. II. Stoddard, has 

 made still further tests with four strains of 

 potato blight obtained from different sources, 

 and with two of these (really one, as the 

 other traces back to the same potatoes one 

 season later) has obtained results far beyond 

 anything yet reported. These results were 

 primarily due to the use of a new medium, 

 which gave us for the first time very definite 

 attempts at oospore formation, and with a cer- 

 tain modification of this medium absolutely 

 perfect oogonia, antheridia and even oospores 

 have heen obtained. We have not been suc- 

 cessful, as yet, in producing the oogonia in 

 cultures in anything like the abundance of 

 those of Phytophthora Phaseoli and Phytoph- 

 thora cactorum in the same medium, and very 

 few of the oogonia produce even partially ma- 

 ture oospores, but of their nature there can be 

 absolutely no doubt. Whether or not we can 

 perfect their formation in greater abundance 

 remains to be seen, but recently, from an un- 

 usually good culture, a temporary slide prepa- 

 ration showed over a hundred of these 

 oogonia, mostly without oospores or with im- 

 mature ones; whereas last March the most we 

 could find in similar slides were half a dozen 

 or less. 



From the results of our recent investigation 

 there is no doubt that the curious threads and 

 bodies that Jones, and the writer to a much 

 less extent, previously obtained, were attempts 

 at the formation of oogonia. We should 

 judge, however, that Jones's cultural media, 

 except for one particular, were not suited to 

 perfect these bodies further, and that the ex- 

 cretory markings he obtained on the cell 

 walls were largely abnormal. From my in- 

 vestigations it can be stated that the oogonia 

 of the potato blight are thick-walled, with a 

 more or less roughened or ornamented ex- 



ternal coat, due to excretory thickening of the 

 original wall, and are tinted more or less a 

 chestnut brown. The oospores are moderately 

 thick-walled, smooth and colorless. The 

 oogonia are of a quite different type from 

 those of both P. Phaseoli and P. cactorum, 

 which are similar. The oogonia and oospores 

 of these two are somewhat smaller than those 

 of P. infestans, but the chief difference is 

 their smooth, hyaline, thin-walled oogonia. 



Not only has the writer obtained the 

 oospores of P. infestans in pure cultures, but 

 he has also succeeded in raising what he con- 

 siders crosses of this fungus with both P. 

 Phaseoli and P. cactorum by inoculating a 

 test-tube of the special medium with P. in- 

 festans at the top and one or the other of 

 these two species below. With the growth of 

 the two colonies together there appear in the 

 vicinity of the P. infestans colony not only 

 the oospores of the other fungus but also 

 oospores of the P. infestans type. These 

 oospores of the P. infestans type so far appear 

 only rarely in the crosses with P. cactorum, 

 which, however, have only recently been made. 

 In the crosses with P. Phaseoli the oospores of 

 the P. infestans type are more abundant than 

 they have ever yet appeared under the most 

 favorable conditions in pure cultures of P. 

 infestans, and many of them produced per- 

 fect oospores. On the whole the oogonia and 

 oospores appear to be somewhat larger and 

 less deeply tinted than those from the pure 

 cultures of P. infestans. Crosses between P. 

 infestans and P. Phaseoli made last March 

 still continue to produce oospores of the in- 

 festans type, not usually as abundant as those 

 of the Phaseoli type, however, though these 

 cultures have been renewed six times since 

 their original crossing. These descendants 

 are not from the oospores, since they never 

 germinate in the cultures. 



From the data at hand it looks as though 

 there were not two strains (male and female) 

 of the potato blight, as we suggested some 

 time ago, but that the potato fungus had 

 largely lost its power to reproduce itself sex- 

 ually. This loss may have come about by 

 propagating it year after year asexually 



