GERMINATION STUDIES 6 1 



of tin along the middle of the back and those next to the free outer segments 

 on the ends were folded in vntil parallel with the bottom. These act as a shelf 

 on which to rest the next higher tray. The outer and innermost segments at 

 both ends were bent outward, forming projections which are very useful in 

 lifting the trays. The second segment from the corner at either end was bent 

 out at right angles to the side, and then the outer portion of it was again turned 

 up until it was parallel with the position which it formerly occupied. These, with 

 the segments at both corners along the back, which were left erect, prevent the 

 next higher tray from slipping or sliding. It was found desirable to cut the. 

 bottoms of the trays out, since the rapid absorption of heat by the tin has a tend- 

 ency to increase the condensation moisture on the cover glasses. 



For convenience in use it is necessary that trays be about \ inch narrower 

 than the slides are long. Unfortunately, the slides thus extending over the 

 edges of the pans are very easily struck, and the cultures thereby endangered 

 when one is putting other material into or taking it out of the thermostat. To 

 guard against such accident, as well as for greater ease in carrying, a bottom 

 tray was made \ inch wider than the others, and with a back 5^ inches high. 

 This tray had five segments cut at each end instead of four, and these were 

 turned the same as in the other trays, except that the outermost one was 

 bent in to give greater stability. Shelves were made along the back by cut- 

 ting and folding in the tin at these points. The windows thus formed give 

 free circulation of air. These windows, each 2\ inches long and i inch deep, 

 were so cut that if the pieces of tin freed along three sides had been bent 

 straight inward, they would have formed shelves \ inch higher than those at 

 the ends. But they were doubled in close against the back for an inch, and 

 then turned out until they stood parallel with the bottom of the tray. This 

 gives a little back at the points where the windows occur, and prevents any 

 cultures on the second tray from slipping through these open spaces. For 

 convenience in handling, the bottom was not cut from this first tray as from 

 the others, and it may be used for a support for cultures or not, at the discre- 

 tion of the operator. 



The trays were all made of the same size. Five trays besides the bottom one 

 constitute a "set" as we have used them. Each such set holds 120 cultures, 

 and occupies only 36 square inches of space in the thermostat. The trays may, 

 of course, be made of any length or of any height, the dimensions given are 

 those best suited to the thermostat which we have used. When all the trays 

 have been filled in making up a set of cultures the five upper ones are lifted 

 together and so placed on the lowest pan that their open sides were against 

 the back of this tray. 



I am aware that the number of words necessary for describing this little 

 piece of apparatus makes it appear somewhat complicated, but if one will take 

 a piece of paper of suitable dimensions and follow the description given, he 

 will find that the making of a model of one of these trays is a very simple 

 matter, 



