INTRODUCTION 5 



yield floral development, how the flower looks when the embryo sac 

 is mature; and how it looks after fertilization. 



Such studies add immensely to the value of a preparation. A con- 

 siderable part of a botanical education can be gained by collecting 

 material, making and studying preparations, reading what is available, 

 and thinking. 



Some biologists regard cut and stained sections as a mere mess of 

 artifacts, giving only distorted, misleading views of the actual struc- 

 tures; and it must be admitted that some structures, notably the liquid 

 albuminoids, are changed by the processes of fixing, imbedding, and 

 staining. However, no one knows this better than the expert cytolo- 

 gist. Every student of plant structures should compare the fixed and 

 stained material with the living. Chromosomes in the pollen mother- 

 cells of a lily can be counted and measured and photographed in the 

 living condition; and such details which can be seen in the living con- 

 dition are so like those in fixed and stained material that we believe 

 that finer details, which can be seen dimly or not at all in living ma- 

 terial, are equally well preserved. Chromosomes as small as those in 

 the spore mother-cells of Osmunda cinnamomea can be seen in the 

 living condition, the various stages in mitosis can be traced, and chon- 

 driosomes can be seen moving vigorously in living cells. Protoplasmic 

 connections can be seen easily in living cells of the endosperm of 

 Diospyros discolor, and can be seen, dimly, in the endosperm of a date 

 seed, as one gets it on the market. And so we believe that smaller 

 protoplasmic strands, which cannot be seen in the living condition, 

 but which are easily seen in thin, well-stained sections, are not arti- 

 facts produced by fixing, imbedding, and staining, but are real struc- 

 tures which have merely been made visible by these processes. Of all the 

 structures with which the cytologist has to deal, protoplasm suffers 

 most from fixing and imbedding. But even here, protoplasm, like 

 that in the egg of a cycad, shows the large vacuoles and smaller and 

 smaller vacuoles in the living condition, so that still smaller vacuoles, 

 not visible in the living condition, are no more likely to be artifacts 

 than those so easily seen in the living condition. 



However, all who make preparations for microscopic investigation 

 should be constantly on guard, and should always compare the living 

 material with that which has been subjected to the various processes 

 of microtechnique. 



