i<;7 



used varied from niic fo several weeks. To oliviale at least part of tiiis 

 (litlieuKy I seleetcd a lieavy Itrass tube haviiii; an inside diameter of l..» 

 cm. and a leiijjtli of 120 em. Into this tithe directly (tpposite one another 

 wore threaded air li«ht small hrass luhes having an internjil fliameter of 

 4 mm. au outside diameter 7 mm. and a leii«th of ;") mm. This tube was 

 supported at the center, between two rows of water cultures, by a rinj:- 

 stand. Thi.s arrangement eliminati'd the iueakage that often occurred with 

 the glass T-tubes and by being fastened together in one piece it also elim- 

 inated 27 of the 4;") rubber tubing connections, besides being more convenient 

 in other ways as to neatness, compactness, etc. The F.unsen pump as I 

 have it arranged and when working at full capacity will send through 

 the above mentioned tubes 4 liters of air per uiinute overcoming at the 

 same time the resistance offero<T by a column of water 20 cm. in depth. 

 This would amount, if the pressure of the water mains remains constant, to 

 240 liters per hour or 5.760 liters per day when the pump continues to work 

 at full capacity. As. however, only about one liter i)er hour w^as generally 

 used, at this rate, about 240 separate cultures could be aerated simultan- 

 eously with this apparatus if properly arranged and adjusted. This will 

 depend, as before mentioned, somewhat on the size of the glass tubes which 

 conduct the air through solutions in the culture jars. If these tubes are 

 ver.v small or much constricted at the end so as to make small bubbles, 

 which i.s desirable, so much back pressure will be generated in moving a 

 large quantity of air that most of it will escape at the pump. In my experi- 

 ments so far. however, only about seven to fifteen cultures have been aired 

 at once and such a size of tubes used that the difficulty just mentioned did 

 not occur. 



A STUDY OF POLLEN II. 



F. M. Andrkws. 



Since the appearance of the first of these two accounts on investigations 

 made on pollen of various kinds, further studies have been in progress in 

 order to study stmie of the points there indicated on a greater number of 

 plants. In the first paper which appeared in 1917 I had investigated 435 

 plants. Since that time I have extended my study of the pollen so that 

 now I have investigated 508 plants. This list of phanerogams include 

 plants of many and distantly related families all of which have been sub- 

 jected to the same conditions in order to ascertain how their pollen would 

 behave. All of the pollen of these plants, as in the first paper, have been 

 put under favorable cultural conditions in cane sugar. This medium was 

 supplied to them in solutions of different strengths from weak to strong. 

 Of the T.i plants so investigated since my first account appeared in 1017, 

 about the same proportion of plants showed a response as there indicated. 



