THE EMBRYO 319 



even fertilization often occurs in the "ripe," fruitlike "seeds" of Ginkgo, 

 as they lie on the ground. No dormant period is present in viviparous 

 taxa and in many tropical genera; there is none in many aroids — 

 Peltandra, Orontium, Anthurium — and in the Hydrocharitaceae — 

 TJiulassia — and in other aquatic taxa. The coconut palm, Cocos nucifera, 

 has long been known as an example of embryo development in a seed 

 on the ground. When the ripe coconut falls to the ground, the embryo 

 is an undiflFerentiated, cylindrical body about 8 mm long. The embryo 

 continues to grow, apparently without resting, and the plumule breaks 

 through the husk after about four months. In Cocao and Thalassia, the 

 embryo continues growth through the germination stage while within the 

 fruit, and the germinating seeds are set free to continue growth when the 

 fruit disintegrates. Dormant seeds are characteristic of most angio- 

 sperms, but, in many, the embryo is not dormant. Studies of this intra- 

 seminal growth are few, and its extent among angiosperms is little 

 known. That the seeds of many genera of the Ranunculaceae have un- 

 differentiated embrvos at shedding is common knowledge, and probably 

 many other herbaceous genera — both dicotyledonous and monocotyle- 

 donous — have seeds of this type. This type has been described in Crocus, 

 several genera in the Fumariaceae, Papaveraceae, Umbelliferae, and, in 

 woody plants, in Fraxinus. In Anemone, the embryos of different species 

 are at various stages of development at seed shedding, and, conse- 

 quently, seeds with well-developed embryos germinate early; those 

 with undeveloped embryos, months later. 



Continuation of embryo growth within the seed after shedding is 

 apparently not related to soil type, but presence and absorption of 

 water are usually necessary, and presence or absence of light and 

 freezing may affect development. The seeds of many aquatic genera 

 require continuous submersion in water. Seeds of some taxa continue 

 this intraseminal growth unbroken at time of shedding; in others, there 

 may be a long period when the immature embryo lies dormant before 

 completing growth. Examples of time reported necessary to complete 

 growth from seed-shedding stage to germinating stage are: Fiimaria, 

 eight days; Caltha, ten days; Clematis, seventeen days; Actaea, 

 Thalictnim, Hepatica, two months; Fraxinus, Cocos, Paris, four months; 

 Crocus, six months; Conjdalis, ten months; Trillium, twelve months. The 

 seed of Ranunculus Ficaria is described as not germinating until the 

 second spring after it is shed. Measurements of length of embryo while 

 still within the seed show rate of intiaseminal growth: in Eranthis, May 

 —100 IX, June— 225 ^i, July-^30 fi, September— 1000 p., November— 

 3000 i^i; in Conjdalis, May — 150 /x, October — 1000 jx; in Rominculus 

 Ficaria, May — 100 ^a, October — 625 /x. Embryo development within 

 seeds may be the continuation of growth in process at time of shedding 



