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percentages to be due to changes in external conditions, to which, per- 
haps, the forms are peculiarly responsive. The ease and certainty with 
which high germination percentages were secured in other families cer- 
tainly lends support to the view. ; 
The experiments are still in progress, as there are still many points to 
be worked out in detail. Among them are the effects of varying soil tem- 
peratures, of a wider range of soils, of progressive experiments for the 
determination of resting periods in the various forms, of duration of via- 
bility, of the effect of freezing, and others self-suggestive to the experi- 
mentalist. Until these are worked out in detail the question as to the 
causes of the relatively small distribution of any given composite form 
must remain open. So far as the experiments go they point to this limita- 
tion being due in a very large degree: 
1. To a low germination percentage, largely due to an extreme sensi- 
tiveness on the part of the embryo to external conditions, to which should 
perhaps be added imperfect pollination, due to causes already given. 
2. To an extreme sensitiveness of the seedlings to temperature and 
moisture changes, either in soil or atmosphere. This necessarily brings 
about a peculiar sensitiveness to direct sunlight. 
When the habits of most of our native composites are considered it 
will be seen that this extreme sensitiveness in both achene and seedling 
proves an effectual limitation to their distribution. Other factors than 
these here emphasized enter, but none are of such general application. 
FoRMALIN AS A REAGENT IN BLoop Stupres. By Ernest I. K1Zer. 
Among the most common reagents used in the demonstration of blood 
corpuscle structure, are found osmie acid, salt solutions, picric acid and 
acetic acid. But all of these cause distortions of the corpuscles, so they 
are imperfect fixing agents and preservatives. The method of drying 
blood on the coverslips is seldom successful in the hands of beginners. 
Formalin has been found very useful in this connection, both as a 
fixing agent and as a preservative, because it produces no appreciable dis- 
