Jtjne 2, 1922J 



SCIENCE 



597 



varied from .00013 mm to .00026 mm in diam- 

 eter. The thickness of the water film was prob- 

 ably .0014 mm. He compares these with the 

 diameters of fog particles measured by Barus 

 in his experiments on atmospheric nueleation. 

 He also treats of the sources of solid particles 

 in London fogs. These come quickly, the air 

 being relatively clean at 6 a.m. ; and heavily 

 laden with smoke fog by 9 a.m. When the air 

 in London is fairly clear in winter, the amount 

 of suspended matter is approximately 1 milli- 

 gram per cubic meter; during a dense fog it 

 rises to 5 mgs/m^. A rough estimate of the 

 weight of the impurity in a fog for an area of 

 310 square kilometers (120 square miles) and 

 a height of 122 meters gives 193 tons. Accord- 

 ing to Dr. Owens the amount of smoke pro- 

 duced between 6 a.m. and 10 a.m. from domestic 

 fires and factories is sufficient to account for 

 this load of suspended matter over London on 

 a foggy day at 10 a.m. 



Dr. Owens touches on the amount of dust in 

 expired air. It has been assumed by medical 

 men that the air passage through nose and 

 throat practically trapped all the solid impuri- 

 ties. He doubts this and some experiments 

 which he made seem to prove that in ordinary 

 breathing the expired air contained about 70 

 per cent, of the suspended impurity which en- 

 tered during inspiration. It seems certain that 

 suspended matter is not entirely removed by 

 action of the respiratory passages. In fact, 

 only about 30 per cent, is removed. 



Quite a good deal of space is given to a dis- 

 cussion of the relation of visibility to sus- 

 pended impurity. The discussion is technical 

 and no definite conclusions are reached. 



Research work on measurements of acidity 

 in the suspended matter of air is in progress. 

 Alexander McAdie 



SPECIAL ARTICLES 

 STUDIES OF THE POLLEN TUBES AND 

 ABORTIVE OVULES OF THE GLOBE 

 MUTANT OF DATURA 

 The Globe mutant, like the twelve or more 

 (^ther (2«-M) mutants already described (1 

 and 3), owes its mutant character to the pres- 

 ence of a single extra chromosome, the so- 



matic number being 25 instead of 24. One of 

 us (2) has shown by means of breeding tests 

 that the inheritance of Globes is almost ex- 

 clusively through the ovules, by which it is 

 transmitted to only one quarter of the off- 

 spring whether the parent Globe is selfed or is 

 pollinated by a normal diploid. Pollen from a 

 Globe when applied to stigmas of a normal 

 parent transmits the Globe complex to con- 

 siderably less than 3 per cent, of the offspring. 

 Our colleague, Mr. Belling, finds that half 

 of the pollen grains of Globe plants receive 

 the extra chromosome. The fact that some of 

 the ovules transmit the character, while some 

 give rise to normal plants, indicates that a 

 similar segregation takes place in the forma- 

 tion of the ovules. While the back-cross of 

 Globes X normal pollen does not produce more 

 than about one quarter Globes in the offspring, 

 there are more than enough small aborted 

 ovules in the seed pod to account for the miss- 

 ing Globes necessary to satisfy the expected 

 1 :1 ratio of Globes to normals. We may 

 safely infer, therefore, that half of the ma- 

 ture megaspores within the ovules receive the 

 extra chromosome. 



If there were no losses through bad pollen 

 or abortion of ovules, the expected result of 

 selfing (2m+l) Globes would be 25 per cent, 

 normal diploid plants with the formula 2n, 

 50 per cent. (2w+l) Globes, and 25 per cent. 

 (2w-|-2) Globes with two extra chromosomes 

 in the Globe set. Instead, we get mostly nor- 

 mals, with only about 25 per cent (2w+l) 

 Globes and but rarely a (2w+2) Globe. 



The problem here is to find if possible ex- 

 actly where the losses are incun-ed, whether 

 in pollen gi'ains which fail to germinate, in 

 pollen tubes which fail to grow fast enough 

 to reach the ovary, or which fail to fertilize 

 the ovules, or entirely in zygotes which are 

 lost in the aborted ovules. 



Aborted ovules were counted in seed pods 

 that were nearly ripe. These can be seen 

 with a hand lens or binocular dissecting micro- 

 scope on the enlarged fleshy portion of the 

 placenta} among the seeds. 



Two classes of aborted ovules were recog- 

 nized, the tiny apparently unenlarged ovules 

 and those that were distinctly enlarged. The 



