PTERIDOPHYTA. 199 
In ancient geological times the Calamites and their allies consti- 
tuted a distinct order (Calamariez) of tree-like plants 3 metre in thick- 
ness and ten metres in height. 
Practical Studies.—(a) Collect in early spring a number of cone- 
bearing stems of the Common Horsetail. Note the joints (nodes), 
bearing whorls of united flat leaves, and the cone, composed of whorls 
of shield-shaped leaves. Split the cone and stem and note that the 
latter is hollow, with closed nodes. 
(0) Carefully dissect out a single shield-shaped leaf from the cone, 
and examine it, using a low power. Note the sac-shaped spore-cases 
upon the under side of the leaf. Mount some of the spores dry, using 
no cover-glass, and examine with the 4-inch objective. Breathe upon 
the spores very gently to moisten them, and notice the coiling of the 
elaters; observe the quick uncoiling which takes place upon the 
evaporation of the moisture. 
(c) Sow a quantity of the fresh spores upon moist earth or porous 
pottery, covering with a bell-jar and taking every precaution to secure 
constant moisture. The spores will begin to germinate in a few days, 
when studies of successive stages of growth may be taken up. By 
care the mature plants of the first stage (prothallia) may be grown, 
and the antherids and archegones studied. 
(d) Make very thin cross-sections of the stem of the Common Horse- 
tail. Note the position of the fibro-vascular bundles. Now make 
vertical sections of the bundles and study the tissues, using high 
powers. 
(e) Study the breathing-pores on the green stems of the Common 
‘Horsetail. Compare these with those of the Scouring Rush. Study 
also the disposition of the chlorophyll-bearing tissue in cross-sections 
of both stems. : 
(f) Examine underground stems of Horsetails, and compare the 
structure with that of the aerial stems. Make cross-sections of the 
roots which are attached to these underground stems. 
Crass I. Fizicinz (the Ferns). 
418, Here the plant-body consists of a solid stem, bearing 
roots and broadly expanded leaves, the latter usually long- 
stalked. The stems are mostly horizontal and under- 
ground, but in some cases they rise to a considerable height 
vertically in the air. 
