. Studies on the plant cell. Plant cells and tissues. 372 THE AMERICAN NATURALIST. [Vol. XXXVIII. effect is that of a much coiled and twisted thread whose loops are united at intervals to form large and small meshes. The ground substance of this thread is called linin and imbedded in it as in a matrix are deeply staining granules of chromatin. Chromatin is regarded as the most important substance in the nucleus, ' chiefly because of its behavior during nuclear division, and in critical periods of the life history of organisms as at sporogen- esis, gametogenesis and -fertilization (to b
. Studies on the plant cell. Plant cells and tissues. 372 THE AMERICAN NATURALIST. [Vol. XXXVIII. effect is that of a much coiled and twisted thread whose loops are united at intervals to form large and small meshes. The ground substance of this thread is called linin and imbedded in it as in a matrix are deeply staining granules of chromatin. Chromatin is regarded as the most important substance in the nucleus, ' chiefly because of its behavior during nuclear division, and in critical periods of the life history of organisms as at sporogen- esis, gametogenesis and -fertilization (to be described in Section V). Just before nuclear division the chromatin becomes organ- ized into bodies named chromosomes which are remarkably uni- form in number and definite in shape for each tissue and period of the plant's life. They will be discussed under " The Events of Nuclear Division " (Section II), and in Sections IV and Fig. I.—The resting nucleus, a. Embryo sac of lily with linin thread and two nucleoli. ^,.Root of onion large nucleolus., c, Tetraspore of Corallina showing large chro- matin body and small nucleolus. oT, Spirogyra with central body containing chroma- tin, e. Chromatin on linin net work from egg of pine. After Mitzkewitsch and Chamberlain. In the meshes of the linin network or lying freely in the nuclear sap may be found one or more bodies, generally globular in form, called nucleoli. (See Fig. i a and Fig. i b). The nucleolus is generally regarded as a secretion of the nucleus and it is quite certain that its substance is utilized just previous to and during the period of nuclear division when the spindle is formed. (Strasburger '95 and : 00, p. 125, and from the work of others). The structure is not always homogeneous but may show in the interior small vesicles or areas of a different con- sistency from the periphery. There is often present also a rather thick outer shell or membrane. Sometimes the chromatin in the nucleus may be gath
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