REPRODUCTION. 237 



the seedlings of Cruciferce and Papilionacece., which are without 

 endosperm, present physiologically similar structures in the much- 

 thickened cotyledons (rich in oil). 



AVe will not enter into a discussion of the arrangements for the 

 ejection of seeds from the ovaries and fruits. We will only men- 

 tion a peculiarity of the seeds of Erodium, namely, under favorable 

 circumstances they are forced into the ground by the movements 

 of the hygroscopic awn. In Arachis hypogcea (peanut) the basis of 

 the ovary grows downward, carrying the young ovary into the soil, 

 where it matures. Some of the mechanical movements will be 

 more fully explained in the chapter on the phenomena of move- 

 ments. 



Germination. 



Germination takes place after the period of rest, provided there 

 is sufficient moisture^ a teinperature varying, as a rule, from 6° C. to 

 45° C. (Sachs), and air (O). Light is therefore not necessary. 

 The appropriation of oxygen will be discussed later. 



The duration of the viahility of seeds is limited, but diifers 

 greatly in different plants. Some seeds must be placed in the soil 

 at once (coffee), many others can germinate at once or later; some 

 remain viable only during one vegetative pause (winter) ; others 

 several or many years. The reports that seeds one thousand or two 

 thousand years old were still capable of germination, are questionable. 

 Many seeds can not germinate immediately after their separation 

 from the mother-plant. According to Sachs, potatoes and onions 

 cannot send out shoots during November or December of the same 

 season in which they were formed. 



The subject of the ' ' rest-period ' ' of seeds as well as ' ' rest ' ' 

 in general (tubers, bulbs, buds rest also) is more difficult of explana- 

 tion than one would suppose. The following statement is accord- 

 ing to tlie authority of Sachs * : We may assume that seeds, Ijiilbs, 

 etc. , which are capable of germinating at once receive the neces- 

 sary amount of ferment during their formation while still con- 

 nected with the mother-plant ; in other cases a longer period (and 

 perhaps lower temperature) is required to form the necessary fer- 

 ment. These ferments (as, for example, the starch-dissolving dias- 



' Vorlesungeu, p. 435. 



