_Cruciferae_, _Ribes_, _Vaccinium_; (5) parenchyma with thickened, cellulose walls, _Geranium_, _Viburnum_; (6) a single row of stone-cells, _Labiatae_; (7) tissue of stone-cells, _Hippuris_, _Naias_, _Potamogeton_; (8) elongate stone-cells, _Coniferae_, _Cupuliferae_, _Euphorbia_, _Linum_, _Malva_, _Viola_; (9) short, columnar, thick-walled branched cells, _Cucurbitaceae_, _Datura_, _Hypericum_; (10) prosenchyma with cellulose walls, _Clematis_; (11) prosenchyma with lignified walls, _Fraxinus_, _Rhamnus_, _Ranunculus_. The seed coats have a certain influence in determining germination at the proper time, inasmuch as they make it difficult for the seed to germinate under the stimulus of a quantity of warmth and moisture insufficient to support the seedling. The effect of the endosperm, as well as that of other food supply in the seed, upon germination and the establishment of the seedling is obvious. The behavior of seed or spore with respect to germination depends in a large degree upon the character of the protoplasm or embryo, though in just what way is at present a matter of conjecture. It is evident that many seeds are not viable because fertilization has not been effected, and in consequence no embryo has developed. This is the usual explanation of the low germinating power of the seeds of some species, especially polyspermatous ones. But even in viable seeds the behavior is always more or less irregular. The seeds of some species will grow immediately after ripening, while others germinate only after a resting period of uncertain duration. The same is true of spores. Even in the case of seeds from the same parent, under apparently similar conditions, while the majority will germinate the first year, some will lie dormant for one or more years. The precise reason why many seeds and spores germinate more readily after being frozen is equally obscure. The period of time for which disseminules may remain viable is extremely diverse, though, as would be expected, it is much longer as a rule for seeds than for spores. The greater vitality of seeds in the case of ruderal plants suggests that this diversity may be due simply to variation in the vigor of the embryos. It would seem that under proper conditions seeds may retain their viability for an indefinite period.