PTERIDOPHYTES—LY COPODI ALES 
245 
The growing points of stems and roots cut easily in paraffin, and 
when the material becomes too hard to cut in paraffin it can be cut 
without any imbedding. It is easier to get good sections of L. lucidu- 
lum and L. inundatum than of drier species, like L. obscurum and 
L. clavatum. Safranin and Delafield’s haematoxylin is a reliable 
stain. Safranin with anilin blue or light green is also good, and the 
light green gives particularly clear views of the phloem. 
If young sporelings are available they afford a beautiful example 
of a very primitive type of stele, in transverse section showing an 
exarch protostele with 4 or 5 radiating arms of metaxylem, each 
tipped with a comparatively large group of protoxylem cells. In 
most species, this simple radial stele of the sporeling passes into a 
complicated, banded stele in the adult plant. Even in the adult 
plant the protoxylem and metaxylem are easily distinguished in 
sections near the growing point of the stem or root (Fig. 78). Not 
only in Lycopodium, but in any vascular plant, sections at this age 
are useful in pointing out the protoxylem. 
Sections of the stem and root of Lycopodium complanatum, 
mounted on the same slide, show an interesting parallelism of 
structures. Transverse sections of the stem of Lycopodium pithyoides, 
a Mexican species, show not only the stem structures but excellent 
transverse sections of roots which grow down through the cortex. 
The strobilus. —For longitudinal sections, cut a slab from each 
side of the strobilus to insure fixing and infiltration. If a strobilus, 
or similar organ, is simply halved, both pieces are likely to curve. 
Among north temperature species, Lycopodium inundatum is the most 
easily cut. A young strobilus 1 cm. in length may show all stages 
from the archesporium to the spore mother-cell. Iron-haematoxylin 
is the best stain for differentiating the archesporial cells. The divi¬ 
sions in the spore mother-cell stain intensely, so that care must be 
taken not to overstain. 
Strobili of Lycopodium dendroideum or L. obscurum 6 or 7 mm. 
in length show a beautiful series in the development of the sporangium 
from the earliest stages up to tetrads. These young stages fix well 
in chromo-acetic acid, with or without a little osmic acid. 
The gametophyte. —In most species the gametophyte, or prothal¬ 
lium, is subterranean, tuberous, and has no chlorophyll; in other 
species the prothallium is partly subterranean and partly aerial, the 
aerial portion being green and bearing the archegonia and antheridia. 
