March 5, 1920] 



SCIENCE 



247 



Uredo Arachidis, althougli a single collection 

 from Paraguay would indicate that it should 

 be called Puccinia Arachidis. It has been 

 known to mycologists since 1884, but only very 

 recently has it attraoted attention of the culti- 

 vator. Specimens received by the writer from 

 W. Eobson, of Montserrat, British West 

 Indies, show every leaf covered with the 

 abundant brownish-yellow powder of the 

 fungus. This was in September, 1916. Mr. 

 Eobson reports that some seasons it is a 

 serious menace to the peanut crop in that 

 island. Experiments for its control with 

 Bordeaux mixture did not prove promising. 



The life cycle of the rust has not been 

 worked out, but as in the case of the chrysan- 

 themum rust the cultivator will meet only 

 with the uredinial stage, for only one kind of 

 spore is produced on cultivated plants. The 

 rust appears to be working its way northward, 

 having been reported from Porto Eico in 1913, 

 and from Cuba in 1915. It has not yet been 

 reported from any part of the United States 

 proper. 



The second rust, to which attention should 

 be called, is one on potatoes and tomatoes 

 (Puccinia PHtieriana) . Little is yet known 

 about it. It was collected by H. Pittier on 

 the wild potato in 1903 and again in 1904 

 on the slopes of the volcano Irazu in Costa 

 Eica, at an altitude of about 10,000 feet, and 

 was found again in the same region by E. W. 

 D. Holway in 1916. It is mentioned in 

 Pittier's " Plantas Usuales de Costa Eica " 

 under the name Uredo Pittieri. More recently 

 specimens have been examined by the writer 

 sent by A. Pachano from Ambato, Ecuador, 

 where it was found in 1918 in the gardens of 

 the Quinta Normal on both potatoes and 

 tomatoes. 



Eor this rust only one kind of spore, the 

 teliospore, is produced in the life-cycle, and 

 these spores germinate at once upon reaching 

 maturity, requiring no period of rest. The 

 habit of the fimgus and its mode of distri- 

 bution are essentially those of the hollyhock 

 rust. In gross appearance, as well as in other 

 characters, it is very similar to the common 

 rust on cocklebur. 



The two rusts, to which attention is partic- 

 ularly called, have not yet demonstrated their 

 full capacity for harm, but from their appear- 

 ance, and from what we know of the intro- 

 duction and behavior of similar rusts that are 

 highly destructive, there seems little doubt 

 that if once established in a region where 

 suitable crops are extensively grown, they 

 will prove most unwelcome to the cultivator. 



J. C. Aethue 



Pdkdde Universitt, 



XiATATETTE, IND. 



THE FIXATION OF FREE NITROGEN BY 

 GREEN PLANTS 



In spite of a considerable amount of nega- 

 tive evidence, the question of the ability of 

 chlorophyll-containing plants to utilize the 

 uncombined nitrogen of the air is still an 

 open one. A large number of experiments 

 with lower forms, especially the grass-green 

 algae, tend to disclaim any such ability and it 

 has come to be very generally accepted that 

 members of the Chlorophycese are not able to 

 use free nitrogen. However, the number of 

 species which have been investigated is small 

 and the culture methods employed have not 

 always been those which are most favorable 

 for the best growth of these organisms. Ac- 

 cordingly experiments were begun in this lab- 

 oratory a few years ago for the purpose of 

 extending our knowledge over a larger number 

 of species, under culture conditions which 

 would insure a rapid and vigorous growth. 

 Some of the results of these experiments are 

 presented in this brief preliminary note and 

 a more detailed account will appear elsewhere 

 within a few months. 



Seven species of grass-green algse (Chloro- 

 phyceae) were used in the experiments. With 

 the exception of one {Protococcus sp.), all 

 were isolated from soil and all species were 

 used in pure culture, understanding by this 

 term a single species free from all other 

 organisms. The ctdtures were grown in 500 

 c.c. Kjeldahl flasks on approximately 150 gr. 

 of accurately weighed mineral nutrient agar. 

 Since previous experiments have shown that 

 these forms will not grow in the complete 



