Studies in the Morphology of Selaginella pumila, Spring. 203 
a, b). All such secondary axes arise on one side only of the hypocotyl, and 
their roots grow down through the air for about 2 mm. before striking the 
soil (fig. 5). Attempts to induce the formation of adventitious roots at 
other points by means of cuttings or layerings have been unsuccessful. 
With a little care the secondary stems with their roots can be removed, 
leaving the primary stem with the cotyledons and trident root-system 
intact (fig. 7). Both primary and secondary stems may remain unbranched 
above or produce in one plane a varying number of short lateral branches 
Fig. 4. Fig. 6. 
each ending in a cone. One or more of the secondary stems may eventually 
overtop the main stem. The secondary roots may also branch laterally. 
The detailed anatomy of the tissues from which these secondary axes 
and their roots originate, also the minute structure of the growing points of 
root and stem, will be dealt with in a later paper. 
The symmetry of erect and evenly illuminated shoots is radial. The 
leaves are all of the same size, and are arranged in four vertical rows along 
the surfaces of the four-sided stem. Though at first sight the phyllotaxy 
appears to be somewhat irregular, it is found on examination to be a modi- 
fication of the usual decussate arrangement. The two leaves belonging to 
each pair do not arise at exactly the same level, and later may become more 
or less widely separated as the result of the elongation of the intervening 
