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METHODS IN PLANT HISTOLOGY 
The Strobilus. — E. arvense affords the most favorable material 
for a study of the development of sporangia, since the strobilus con¬ 
tains almost no silica and, even in its latest stages, is easily cut in 
paraffin. In this species, the young strobili, in the Chicago region, 
can be distinguished from vegetative buds in July; sporogenous 
tissue is well advanced by the middle of August; and the reduction 
divisions occur late in August or early in September (Fig. 80). The 
Fig. 80. Equisetum arvense: A, section of a sporangiophore showing beginning of sporogenous 
tissue, early August condition; B, topography of the strobilus at this stage. A, X580; B, X8. 
spores are not shed until the following April. If you know a patch 
of this species which “fruits” every year, dig up the horizontal 
underground stem in July. The tip of the main axis is almost sure 
to be a strobilus. Dissect away the scale leaves and fix the strobilus 
in chromo-acetic acid with a little osmic acid. August and September 
stages are easy to recognize. If strobili are brought into the labora¬ 
tory in December or January, they shed their spores within a week. 
The spores of Equisetum are excellent for illustrating hygroscopic 
movements. Shake out the spores from the strobili and let them 
dry thoroughly. They can be kept dry for years. When wanted 
