ASSIMILATION AND METASTASIS. 643 



are best known in this respect, show how the reserve-materials of the endosperm 

 may pass into the absorbing organs (in this case ahnost always foliar structures) 

 without there being any actual cohesion of the absorbing organ with the endosperm ; 

 they only lie in close apposition, and can be separated without any injury (as in 

 Ricinus, Fig. 442). It cannot be doubted that the metamorphoses which take place 

 in the nutrient endosperm are brought about by the absorbing organ, that is by 

 the embryo itself; the behaviour of the endosperm of the germinating date, which 

 is absorbed by the delicate tissue of the absorbing organ belonging to the coty- 

 ledon, shows clearly that the hard thickening-layers of the cell-walls of the endo- 

 sperm are first of all transformed into sugar under the influence of this organ, 

 and then absorbed. A substance evidently passes out of the absorbing organ into 

 the endosperm which causes this metamorphosis of the cellulose. The oil and 

 albuminoids of the endosperm are at the same time taken up into the embryo, 

 where all the conducting parts of the parenchyma are filled with sugar and starch 

 as long as the endosperm is not entirely absorbed. In the same manner also 

 in Grasses substances possibly pass out of the embryo into the endosperm, and 

 there bring about the chemical metamorphosis and solution of the starch and albu- 

 minoids before they are absorbed by the scutellum which is applied to the surface 

 of the endosperm. It is possible however that in this case there may be agents 

 capable of bringing about the solution of the starch and gluten in the presence 

 of water independently of any chemical action of tlTe embryo. 



The absorbing roots of parasites penetrate into the tissue of the host, and 

 often grow into it in the most intimate manner. It is certain that the exciting 

 cause of the transport of the products of assimilation from the host to the parasite 

 resides in the latter; the parasite acts on the conducting masses of tissue of the 

 host like a growing bud of the host itself; the food-materials penetrate into it 

 because it consumes and changes them. 



The influence exerted by the absorbing organ of the embryo on the substances 

 in the endosperm, dissolving and chemically changing them, points to the way in 

 which the absorption of food-material is effected by saprophytes which possess no 

 chlorophyll, their absorbing organs probably first causing the solution and chemical 

 transformation of the decaying organic constituents of the humus. The decaying 

 foliage in which Monotropa, Epipogium, and Corallorhiza grow, does not give up 

 to water the serviceable materials which are still present in it, any more than the 

 cellulose of the endosperm of the date, or the starch of the endosperm of Grasses, 

 or the oil of the seed of Ricinus, can be extracted by water ; but these saprophytes 

 nevertheless obtain their nutriment from them. The fact that the roots of plants of 

 this kind are so few in number and so diminutive in length, as in Neottia, or are 

 entirely wanting, as in Epipogium and Corallorhiza, is very remarkable in connection 

 with this. These plants are concealed in the nutrient substratum till the time of 

 flowering, and may act upon it by their whole surface ; and it is important to note 

 that the absorbing surface of seedlings is very small in proportion to the great 



i86i,p. 3). Those parasites which are apparently destitute of chlorophyll (like Orobanche), and 

 saprophytes (as Neottia) contain, according to Wiesner (Bot. Zeitg. 1871, p. 37), traces of chloro- 

 phyll, which however can hardly be taken into account in assimilation. 



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