HAUSTORIAL ORGANS OF SEEDLINGS 



249 



peculiar appearance in longitudinal section, because its upper margin 

 grows out as a sort of fringe or crest bearing absorbing cells on 

 both sides. 



Apart from the Grasses, a highly organised absorbing tissue has been 

 described only in the seedlings of Commelynaceae. In Tradeseantia 

 erecta the knob-shaped end of the 

 filiform cotyledonary stalk remains 

 embedded in the seed. This 

 haustorial organ (Fig. 97 b), which 

 is about the size of a pin's head, 

 is covered on all sides by a layer 

 of specialised absorbing elements ; 

 the latter, which are about '07 mm. 

 in height and 03 mm. in width, 

 contain a large amount of proto- 

 plasm, and are quite loosely con- 

 nected together (Fig. 97 c). 



In the case of starchy seeds 

 the absorbing tissue of the ger- 

 minating embryo secretes an amy- 

 loclastic enzyme, diastase, and thus 

 helps to render the stored-up 

 starch available for absorption. 

 This process is analogous to the 

 secretion of acid substances by 

 root-hairs. If the embryo of a 

 germinating grain of wheat is 

 carefully separated from the en- 

 dosperm, and a paste of wheat- 

 starch and water spread thinly 

 upon the back of the scutellum, 

 the great majority of the starch- 

 grains will become extensively 

 corroded by the action of the 

 exuded diastase in the course of 

 twenty-four hours. A similar 

 corrosion occurs though more 

 slowly if the experiment is carried 

 out upon the club-shaped haustorial organ of Camia indica. It should 

 be noted that, in the case of Grasses, the secretion of diastase is not 

 confined to the absorbing tissue of the scutellum ; this point will be 

 more fully discussed in a subsequent chapter (Chap. X., n., B. 2.). The 

 principal enzyme secreted by the haustorium of the Date and other 



A. Very young sporogonium (embryo) of Dcndro- 

 ceros cichoriacev.s. B. Slightly older sporogonium 

 of D. cnspatus. C. Still older .sporogonium of 

 D. crispatus. d, foot (haustorium) with its tubular 

 absorbing cells. After Leitgeb (from Engler- 

 Prantl, NatUrliehe Pflanzenfamilien). 



