344 Mottier.- — On the Prophases of the Heterotypic Mitosis in 
bare the ovules to the direct contact with the fixing fluid, while in still 
others, not only were the ovules exposed but a part of their chalazal 
ends were cut away, as will be seen, for example, from Figs, i a and %a. 
From this method of preparation, it will be seen that in case the ovule 
is exposed, or if a portion be cut away from the chalazal region, the 
fixing fluid will more readily penetrate the large megaspore mother-cell. 
Long experience with the tissues of higher plants in the use of the three- 
acid mixture, as well as of other fixing reagents, has shown that cells 
thus treated present slightly different appearances in certain structural 
details of cytoplasm and nucleus, and in the readiness with which stains 
are retained by these structures. If the fixing fluid must first pass 
through a layer of tissue of considerable thickness before reaching a given 
cell, the effect of the osmic acid upon that cell, as shown by structure 
and staining qualities, will be somewhat different than had the fluid 
a more direct contact with that cell. Experience has demonstrated also 
that, whenever cells to be studied are embedded any considerable depth 
in a tissue, there is likewise danger in cutting away too much, assuming 
that one operates with a fixed strength of the killing fluid. It is always 
to be understood that when cells show poor or faulty fixation, such pre- 
parations are not used as evidence in support of a conclusion. What is 
good, and what constitutes poor or faulty fixation, are matters to be 
determined by experience. Practice must also determine how material 
is to be prepared for any given reagent of known or unknown merit as 
tested for a similar tissue. 
In order that any effect of preconceived ideas of the author may be 
eliminated in the preparation of the illustrations, he has had the draw- 
ings of the nuclei made by an artist who has been thoroughly trained 
in microscopic observation, and a careful comparison of the preparations 
and the respective drawings shows that each illustration is a very faith- 
ful representation of the object. In this connexion it gives me pleasure 
to acknowledge my indebtedness to Miss Carolyn A. Black for making 
the drawings of the nuclei. 
Observations. 
With the foregoing remarks on methods, we are now ready to pre- 
sent the results of observations. As mentioned in a foregoing paragraph, 
Lilinm Martagon and L. candidum furnished the material for study. 
Even before the inner integument of the ovule is apparent, the mega- 
spore mother-cell is conspicuous because of its large size and the density 
of its contents. 
Both cell and nucleus now begin their period of rapid growth. At 
first the rate of growth of cell and nucleus seems to be equal. When 
the inner integument has begun to grow up about the nucellus (PI. XXIII, 
