246 ABSORBING SYSTEM 



up to its outermost layer, sometimes even extending into the micropyle. 

 According to Koorders, the large absorbing vesicles that appear on the 

 proximal portion of the suspensor of Tectona grandis represent modified 

 cells of the endosperm, which have become secondarily fused with the 

 suspensor. Thus structures which are by no means homologous may 

 serve as haustorial organs in one and the same plant. 



Attention must next be directed to the absorption of reserve- 

 materials during the process of germination. Where the whole of the 

 stored up plastic material provided by the mother-plant for the use 

 of the offspring is contained within the confines of the embryo in 

 which case it is usually deposited in the cotyledons the transitory 

 parasitism of the young plant produces little or no effect either upon 

 its external form or upon its internal organisation. Special arrange- 

 ments for absorption only occur, where the reserve-materials are 

 deposited in tissues, such as the endosperm or more rarely the 

 perisperm which are not in organic connection with the embryo. In 

 such circumstances, namely, the germinating embryo has to extract its 

 plastic materials from foreign tissues, like a genuine parasite ; for this 

 purpose it develops absorbing tissues, and in cases of greater specialisation 

 provides itself with definite organs of absorption. 



Where the embryo is entirely surrounded by the storage tissue, it 

 generally absorbs the soluble food materials through every part of the 

 surface which is in contact with that tissue ; it is more especially the 

 protodermal tissue of the cotyledons that is at first actively engaged 

 in absorption, whereas later the same layer becomes converted into a 

 typical epidermis. This primitive arrangement provides an excellent 

 illustration of change of function. In such cases there is really no 

 specialised absorbing system. The method of absorption is usually 

 very similar to that just described, when the embryo is attached to 

 one side of the endosperm. In the seeds of Agrostemma Githago, 

 for instance, the lower surface of one of the cotyledons is the only 

 part of the embryo that is in contact with the endosperm ; the 

 superficial layer in this region at first acts as the absorbing tissue, 

 but subsequently becomes converted into an epidermis with stomata, 

 in every respect resembling the epidermal layer that arises directly 

 from the protoderm of the outer cotyledon, which is all along in 

 contact with the testa. The only difference between the absorbing 

 epithelium and the non-absorbing protoderm consists in the fact that 

 the cells of the former undergo distinct radial elongation, a modifica- 

 tion which represents the first step towards the development of a 

 specialised absorbing tissue. 



The embryo agrees with the adult plant in the fact that, where 

 definite absorbing tissues are present, these are located in special 



