1929] Bdbcock-Chiusen : Meiosis in Crepis 403 



reliable than the paraffin-section method. The disadvantages of the 

 smear method are that it wastes much material and therefore cannot 

 be applied to plants with so few pollen motlier cells in the anthers 

 as hybrids often have ; also the acetocarmine smears do not give 

 permanent slides, thus making it difficult later on to check up the 

 results previously obtained. The advantage of the iron-acetocarmine 

 method is the quickness with which it can be handled. Tn many cases, 

 however, the time used for fixing and preparing the sectioned slides 

 is so small compared with the time required for examination of the 

 slides that it does not pay to save a little time in preparing the slides, 

 only to waste it during the examination. Sectioned material is 

 unquestionably much more convenient for examination than smears, 

 where disorder reigns, where seriation of stages is destroyed, and 

 where irregularities of tapetum cells and pollen mother cells, often 

 found in hybrids, escape observation because the general disorder 

 makes it impossible to determine to which type of tissue a certain 

 cell belongs. 



In the hybrid Crepis aspcra X bursifolia the following combina- 

 tions of fixation and staining have been compared : 



Fixations Stainings 



Carnoy (absolute alcohol-clilorufunu- 

 glacial acetic-acid 24 hours) 



' Heidenhaiu 's iron-liaeniatoxylin 1 sec- 

 . iodine-gentian violet C tions 



iron-acetocarmine (smears) 



Carnoy-Nava^hin (Carnoy 5 minutes, \ iodine-gentian violet-orange (sections) 

 followed by Navasliin's formalin- i iron-acetocarmine (smears) 



hromic-acetic acid 24 hours) 



As a fixative, the combination of Carnoy 's + Navasliin's fluid is 

 much superior to Carnoy alone, since the latter causes too great con- 

 traction and destroys too much of the finer structure. Navashin's 

 fluid alone has too little penetrating power and results too often in 

 insufficient fixation, except when it is applied to very small and 

 delicate objects such as root tips. In Viola hybrids, furthermore, the 

 junior author has been able to compare Navashin's fixative with the 

 combination of Carnoy 's and Navashin's fluids and the latter has 

 proved, in a number of cases and for this material, to be much better 

 than Carnoy alone. It preserves the fine structural details and the 

 objects are thoroughly fixed. In Crepis this fixative together with 

 the iodine-gentian violet staining gave clear indication of the inner 

 structure of the chromosomes. 



