August 1, 1895.] 



KNOWLEDGE 



173 



the commencement of germination shows a somewhat 

 different state of affairs. The main part of the embryo 

 lives oTitside the seed-coat ; the endosperm has decreased 

 in amoimt, and a part of the cotyledon is closely applied 

 to it. As the embryo increases in size, the endosperm 

 gradually decreases, until it finally disappears. From the 

 relative positions of the parts it is obvious that it must 

 have been absorbed by the young plant, and the only way 

 to account for the corrosive action of delicate cells on so 

 hard a material is the assumption that these cells secrete 

 a ferment, and that this dissolves the cellulose, as in the 

 barley grain. Search for such a substance in the date 

 palm has, however, hitherto been in vain. 



Prof. Marshall Ward, in an elaborate paper in the 

 " Annals of Botany,'' shows that he succeeded in isolating 

 a cellulose-dissolving ferment from a fungus called 

 "batrytis," that sometimes causes havoc among lily 

 plants, giving rise to what is known as the lily disease. 

 The threads (hyphfe) of this fungus eat their way into 

 the interior of the li%-ing cells of the host plant. From 

 their tips a brilliant, refringent, viscid fluid is secreted. 

 Marshall Ward cultivated the fungus in Pasteur's solution 

 -^a nourishing fluid containing the constituents of fungus 

 food in a readily available form — and so procured a large 

 number of the fungal liyphro. On squeezing these in water 

 he obtained a large quantity of a fluid containing the fer- 

 ment in solution, for when it was applied to thin sections 

 of the lily stem, the cellulose walls were observed to 

 swell up and become gradually dissolved. 



Starch and cellulose are composed of carbon, hydrogen, 

 and oxygen, the latter two being present in the same 

 proportion as in water, viz., one to eight by weight. 

 Such substances are termed carbo-hydrates. 



Hitherto we have considered only the digestion of these 

 bodies; we shall now direct our attention to enzymes, by 

 whose action complex nitrogenous compounds are 

 rendereddirectly suitable for plant food. The most remark- 

 able, or at least the most interesting, examples are found 

 amongst the so-called insectivorous plants. 



The pretty little Sundew {Ihvsern rotuniH folia), consist- 

 ing of a small root and rosette of reddish-green leaves, 

 nestUng in tufts of sphagnum moss, displays a markedly 

 digestive action, causLngit to resemble the animal stomach 

 in many respects. Its method of capturing and retaining 

 its insect prey was explained in a previous paper in 

 Knowledge. In it, as in other insectivorous plants, the 

 use subserved by its digestive property is quite obvious 

 from a consideration of its habitat. It lives in marshy 

 places, where there is small store of nitrogenous food. 

 The species of Drosera shown in the plats {Dros^ra 

 dichotoma) is not a British fern, but it illustrates the 

 main features of the British species. Insects retained by 

 the viscid fluid secreted by the leaves soon undergo 

 decomposition. The nitrogenous parts of the body are 

 digested — the hard outer skeleton alone is left — and the 

 products of digestion are absorbed by the leaves. After 

 stimulation by the absorption of nitrogenous matter, the 

 secreted fluid contains a ferment and an acid. The 

 ferment in presence of the acid attacks proteids and con- 

 verts them into peptones. The stomach, we previously 

 noted, contains an acid, and a ferment called pepsin, which 

 has the same property as that of Drosera. Pepsin also is 

 only secreted after the absorption of nitrogenous matter 

 by the walls of the stomach. In these respects, then, it 

 appears that the digestion occurring on the tentacles of 

 Drosera is similar to that taking place in our stomachs. 

 It would appear that the ferment of Drosera is the same 

 as, or at least closely allied to, the pepsin found there. 



The leaves oi Pinyuuul-ii rjf/i/nns (the Butterwort), another 



common British insectivorous plant, displays a like action 

 to that of Drosera. Insects captured by the sticky secretion 

 on the upper surface of the leaf are rolled towards the centre 

 by the iucur^■ing margin, which secretes a peptic fluid. 



A photograph of Veuus's Fly-trap (Diomea mmciptda), a 

 native of North Carolina, is reproduced in the accompanying 

 illustration. On each lobe of the leaf are three long 

 jointed hairs, extremely sensitive to contact of a solid body. 



Veaus's Fly-Traii. 



An insect alighting therein and touching one of the hairs 

 instantly finds itself a prisoner, as the lobes immediately 

 close up and clasp tightly the unwilling guest. Glands on 

 the upper surface of the leaf secrete an acid fluid, into 

 which a ferment is poured after the absorption of nitro- 

 genous food. The result is that the captured insect is 

 soon digested, with the exception of the hard cuticular 

 skeleton. The glands are shown in section in Fig. 3, b. 

 They consist of a rosette of cells supported on a very 

 short stalk, bringing them slightly above the level of the 

 other epidermal cells. The section also illustrates the 

 jointed nature of the long hairs. The presence of the 

 joint enables the hair to bend down, and thus prevents it 

 breaking when the lobes become approximated. 



The arrangements for the capture and retention of 

 insects with a view to digestion are very elaborate in the 

 Nepenthes or pitcher plant, a specimen of which is shown 

 in the plate. The winged portion of the leaf (the petiole 

 or leaf-stalk), the tendril, the outer surface of the pitcher, 



