A study of root tips of Trillium, Vicia, Allium, Podophyllum and Tradescantia with methods designed to differentiate the more chromatic from the less chromatic component of the somatic chromosome. The more chromatic constituent maintains the form of a chromonema throughout the nuclear cycle, and at most if not all stages it is embedded in a less chromatic matrix. As the chromosome isolates in early prophase, the contorted chromonema is double, usually with the halves closely approximated and parallel. In at least one genus (Trillium) the metaphase chromosome shows a quadruple structure, a subdivision of the chromonema in each of its halves having begun at some earlier stage. In the daughter chromosome at anaphase, the chromatic element may appear double or single, depending in part on the closeness of association of the two chrompnemata. This condition continues with modifications into telo-phase and probably through interphase. "Alveolation" previously described in the telophasic chromosome is the reappearance of a chromonematic structure ob- scured in metaphase and anaphase by the chromaticity of the matrix. It is uncertain whether the matrix remains distinct from that of the other chromosomes and from the karyolymph during interphase, or loses its identity between mitoses. The matrices of sister chromosomes separating at anaphase are defined by a division at the end of the immediately preceding prophase, whereas, their respective chromonematic constituents are defined by a division in the second preceding pro-phase. If the stage at which the chromonema splits is correlated with the mass of the substance concerned, smaller chromosomes may possess a simpler structure than that shown here.