Methods

Several tips of branches about 1 cm long were stained in Delafield's haematoxylin and embedded in wax. Some of these blocks were cut to give transverse serial sections from the stem tip, and others were cut to give longitudinal serial sections. The sections were placed on slides in series, over-stained in Delafield's haematoxylin and differentiated in acid alcohol, countersigned in eosin (0.5% soln. in 90% alcohol) and mounted in DPX mountant. Most sections were cut at 10μ on a rocker microtome, but one transverse series was cut at 5μ. A thicker piece of stem (1cm × .5mm × .4mm) was embedded, cut in transverse section at 10μ and stained and mounted as above.

In addition, a 1cm length of stem from the tip of a branch was denuded of soft tissues by dipping into "Janola" (a commercial solution of sodium hypochlorite), and the remaining skeleton was washed and stained in a 0.5% soln. of lignin pink in cellosolve for 48 hours. After this time the skeleton was mounted in DPX for observation. Three lengths of stem from the tip to the thicker parts of the branch were also rid of soft tissues by the same method and were stained in the lignin pink soln. for ½ hour. After this time they were removed to absolute alcohol.

From one series of transverse sections of a branch tip, a model of the soft parts (endoderm only) was constructed to illustrate the method of branching of coenosarc tubes within a branch tip. (It was assumed that the growth pattern in a branch tip is indicative of the growth pattern of the colony as a whole).