167 
used varied from one to several weeks. To obviate at least part of this 
difficulty I selected a heavy brass tube having an inside diameter of 1.5 
em. and a length of 120 em. Into this tube directly opposite one another 
were threaded air tight small brass tubes having an internal diameter of 
4 mm. an outside diameter 7 mm. and a length of 55 mm. This tube was 
supported at the center, between two rows of water cultures, by a ring- 
stand. This arrangement eliminated the breakage that often occurred with 
the glass T-tubes and by being fastened together in one piece it also elim- 
inated 27 of the 45 rubber tubing connections, besides being more convenient 
in other ways as to neatness, compactness, ete. The Bunsen pump as I 
have it arranged and when working at full capacity will send through 
the above mentioned tubes 4 liters of air per minute overcoming at the 
same time the resistance offered 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 per hour was 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 
very small or much constricted at the end so as to make small bubbles, 
which is 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. 
BY 
KF. M. ANDREWS. 
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 some 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 73 plants so investigated since my first account appeared in 1917, 
about the same proportion of plants showed a response as there indicated. 
