MECHANICS OF DORMANCY IN SEEDS 
105 
Methods of Securing Dormancy 
As to the mechanism by which delay in germination of mature 
seeds is secured when they are placed under ordinary germinative 
conditions, we will consider the following: (i) Rudimentary embryos 
that must mature before germination can begin ; (2) complete inhibi- 
tion of water absorption; (3) mechanical resistance to the expansion 
of the embryo and seed contents by enclosing structures; (4) encasing 
structures interfering with oxygen absorption by the embryo and 
perhaps carbon dioxide elimination from it, resulting in the limitation 
of the processes dependent upon these; (5) a state of dormancy in the 
embryo itself or some organ of it, in consequence of which it is unable 
to grow when naked and supplied with all ordinary germinative 
conditions; (6) combinations of two or more of these; (7) assumption 
of secondary dormancy. 
Primary Dormancy. — (i) It has been shown that at ripening many 
seeds have immature embryos^^ that must complete their development 
before germination can begin. Such embryos vary from an un- 
differentiated group of cells or perhaps in some cases a fertilized egg 
to mature embryos. A considerable range of immaturity often ap- 
pears in a single species. This seed character appears more or less 
distributed through all the large groups of seed plants as is shown by 
a few illustrations: Gymnosperms — Ginkgo biloba, Gnetum Gnemon; 
Dicots — Eranthis hiemalis, Ranunculus Ficaria, Corydalis cava, 
Stylidium, Gagea arvensis; Monocots — Hymenocallis speciosa, Paris 
quadrifolia, Erythronium denscanis. The maturing of the embryo 
in some of the seeds of this class requires weeks and even months in 
the germinator, and delays germination to that extent. The immature 
embryos of this group must not be confused with those of certain 
saprophytes and parasites that germinate in the immature condition. 
2. So-called hard seeds have coats that entirely prevent absorption 
of water. This phenomenon predominates in the Leguminosae but it is 
also common in Cistaceae and Malvaceae^* and has been observed in 
perhaps a dozen other families. In some species all the seeds of the 
crop are hard but more frequently only a portion. In either case in 
nature the germination of a single crop is distributed over a consider- 
able period, probably in some cases amounting to many years. For 
instance, Nobbe found that red clover seeds placed in water do not 
^3 Goebel. Organographie der Pflanzen, 454. Jena, 1 898-1901. 
" Guppy. Studies in Seeds and Fruits, 585. London, 1912. 
