HUMUS-PLANTS AND PARASITES. 



'3 



take up organic food from the remains of other plants that are becoming 

 decomposed, or obtain it directly from other living plants, to which they are 

 parasitically attached. To the first category, which are usually distinguished as Co- 

 prophytes, but which I, however, prefer to name Humus-plants (saprophytes), l^elong 

 as well-known examples some of our native Orchids — Neoitia, Epipogum, Corallorhiza, 

 and also Laihraa and Monotropa. In these the consequence of the want of chloro- 

 phyll is that the leaves, which are otherwise numerously developed, remain small 

 and scale-like ; since large leaves have only a meaning and object when they abound 

 in chlorophyll, and serve as organs of nutrition. Since, thus, the function of assi- 

 milation is absent, so also is the conveyance of mineral nutritive matters, dissolved out 

 of the earth in corresponding quantities 

 of water, wholly or in part superfluous. 

 Accordingly, such plants have but few 

 roots ; and, likewise, a vigorously de- 

 veloped woody body in the shoot-axes is 

 wanting. The same is also the case with 

 many Parasites, particularly in the genus 

 Orobanche, very rich in species, which 

 though parasitic on the roots of other ■ 

 plants, nevertheless developes some roots 

 in the earth; for the flower stem shoot- 

 ing up above the ground must needs 

 have a certain supply of water, since it 

 loses at least small quantities of vapour 

 for months. The species of Cuscu/a 

 possess after their germination no roots 

 whatever in the earth : by means of the 

 numerous haustoria, which penetrate into 

 the tissue of the host-plant from the long 

 filiform shoot-axes winding around it, 

 they extract not only all food matters, 

 but also the necessary water, the quantity 

 of which is of course extremely small, 

 since the leaves are reduced to minute 

 membrane-like scales. Much more com- 

 plete than in these cases is the degradation of the shoot-formation in those parasites 

 the whole vegetative body of which developes in the tissue of the host-plant 

 until the production of flowers, or, after taking its origin in these, grows forward 

 below ground. This is the case in the BalanophorccB, the HydnorecB, and 

 RafflesiacccE, of which I have already mentioned that the organs penetrating into 

 the nutritive substratum entirely lose the root-form common in the vascular 

 plants. Up to the time when the flower buds arise, one can scarcely distinguish 

 the vegetative body of such plants as a shoot. That we have to do with plants 

 from the group of Phanerogams, is only to be recognised when the flowers' or in- 

 florescences arise ; and these, in their turn, are to be regardeil even in the typical 

 jjlants containing clilorophyll as highly metamorphosed shoots. l>ut even the parts of 



Fig. s^'—f^alanophora fitiig^osa. 7u the root of the Ivost 

 plant on which it is parasitic ; the darker veins are woody 

 bundles wliich run from the root into the tissue of the parasite ; 

 <7, tyC young flower shoots (natural size). 



