CHAPTER XXV 
SPERMATOPHYTES 
A NGIO SPERM S 
If one should master the technic for all features of this group, he 
would be prepared to deal with all the rest; for embryo sacs are so 
delicate that they are as difficult as the free nuclear stage in the female 
gametophyte of a gymnosperm, while the peach stone needs a petro- 
tome rather than a microtome. Between these extremes there is 
everything imaginable in structure, chemical composition, and 
consistency. 
Some hints will be given, but the student will gradually learn 
what should be cut freehand and what should be imbedded; what 
stages in floral development, what stages in the development of the 
embryo sac, or what stages in spermatogenesis are likely to be corre¬ 
lated with easily recognized field characters, and what fixing agents 
are likely to give the best results, with various kinds of material. 
The Vegetative Structures—In stems, roots, and leaves the 
more delicate structures should be imbedded in paraffin and the more 
rigid structures should be cut without imbedding at all; but it should 
be remembered that the range of structures which can be imbedded 
in paraffin can be increased by the use of hydrofluoric acid; and also 
that hydrofluoric acid or cellulose acetate will extend almost indefi¬ 
nitely the range of structures which can be cut without imbedding. 
The stem .—The vascular cylinder of the angiosperms is either an 
endarch siphonostele, or a polystele derived from it. For a study of 
the development of the stem, the common geranium ( Pelargonium ) 
may be recommended. Near the base of a fresh stem, about 1 cm. 
in diameter, cut freehand sections and fix them in 95 per cent alcohol 
for 10 to 20 minutes; transfer to 70 per cent alcohol to extract the 
chlorophyll, and then stain in safranin and light green. Such sections 
will show both primary and secondary structures in the stele and in 
the cortex. Higher up, there will be secondary structures only in 
the stele; and still higher up will be found the origin of interfascicular 
cambium. All these can be cut without imbedding, but the earlier 
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