1580 



A TEXTBOOK OF THEORETICAL BOTANY 



Quite different from the above and interesting because found in Vtcia 

 faba, is the clamp structure described by Orr. The radicle lies in a pocket 

 of the testa, close to, but above the micropyle. On each side of this pocket 

 there is a dark, raised patch, and the surfaces fit very closely against 

 opposite sides of the base of the radicle, the surfaces of both structures 

 being papillate. It is suggested that these are clamps holding the expanding 

 radicle at germination and preventing it from exercising a back-pressure 

 which might rupture the hypocotyl. Experiment shows that this is a real 

 danger. Similar preventions may exist in other seeds. 



Fig. 1440. — Davidia invohicrata. 

 Cornaceae. Germination of the 

 stony fruit. The germinating 

 seeds push off longitudinal 

 valves or shutters in the 

 pericarp. 



Fig. 1 44 1. — Sclevocoryo cajjra. Ger- 

 mination of the tricarpellary stony 

 fruit. The fenestra in the stony 

 pericarp are closed by plugs which 

 are pushed out by the radicles of the 

 germinating seeds within. {From 

 Hill, ''Annals of Botany".) 



The cotyledons of seedlings, appendages of the embryo before germina- 

 tion, have always been the subjects of remark on account of their variety 

 of form and the marked differences which often exist between them and 

 the foliage leaves. In spite of all their modifications there can be little 

 doubt that they are, in fact, leaves, but in many cases, leaves with a repressed 

 development. Some would see in them types of the primitive foliage of 

 their species, and the intermediate stages which are often present, between 

 the cotyledonary form and that of the mature foliage, as recapitulatory 

 phases of a phylogenetic sequence. The fact that in many species, e.g., 

 in Statice, Lysimachia and many Rubiaceae, there is little or no difference 

 between the cotyledons and the foliage leaves, lends support, however, to 

 the view that in other cases the cotyledons have been secondarily modified 



