Filamentous Component (Slime) in Coniferous Sieve Elements
In the literature, it is agreed that in angiosperm sieve elements, a fibrillar, or filamentous, proteinaceous material is present, but the presence of this material in gymnosperms is not agreed upon. Some authors have reported filamentous material (slime) in Pinaceae by light and by electron microscopy. By contrast, some authors have found no structural component in conifers comparable to the sieve element fibrillar component in angiosperms.This report is an affirmation that filamentous material is present in Pinus strobus L. sieve elements. The finest filamentous unit, when measurable, appears to range from 40-60 A in diameter (Fig. 1, arrows). These filaments have a tendency to accumulate to various degrees. Generally, they aggregate in two; then the double structure measures 120-160 A in diameter (Fig. 1, double arrows), although the distance between two filaments is not constant.