18 Botanical Microtechnique 



TABLE 3.2 

 Killing Fluids Based on the Nawaschin and Bouin Formulas 

 (The numbers in the columns represent cubic centimeters of the designated reagents) 



maldehyde before using. A few hours after the formaldehyde is added 

 a perceptible change of color takes place in the licpiid, and after 

 several days the chromic acid becomes changed to an oli\e or green 

 compound. Long before this condition is reached, killing action has 

 been completed, and the altered fluid then serves as an excellent 

 hardening and preserving agent. Material may be left in these fluids 

 for as long as 5 years and yield excellent histological preparations. 

 The effect of prolonged storage on critical cytological details deserves 

 further study. 1 he minimum time for small masses of soft tissue is 

 12 hr., but it is obvious from the foregoing remarks thai several days 

 at least can be allowed to insure hardening without danger of distor- 

 tion or darkening ol the material. A fiuther ad\antage of the Na- 

 waschin txjjc (hiid is that materials need not be sul)se(|uentl\ washed 

 in water, thus axoiding the possil)le softening and pulping ol mate- 

 rial. 



Boiiin's (iuid, gi\en in Table '^2, has long and deser\edl\ been 

 a favorite. It is excellent for loot tips, especially for telophase figures, 

 and has been used successfully for embryo sac studies. The complete 

 mixture is stable and may be kept on hand in the hd)orator^ or 

 carried to the field read) for use. A mininunn iiitcrxal of 12 hi-, is 

 suggested for finely divided material. Larger ))ieces such as thick 

 root ti])S or mature tissues should ]ia\e at least hS hi. I'lolonged 

 storage is regarded as undesirable. Alter the optimum intei\al in 

 the killing fluid, the material is not washed in \vatei. but is rinsed 

 several times in 20% alcohol 01 acetone. Dehydration is then c on- 

 tinned as descril)ed later. 



