250 ABSORBING SYSTEM 



Palms is a cellulose-attacking cytase, in accordance with the fact that 

 the non-nitrogenous reserve material is in this instance represented 

 by the greatly thickened cell-walls of the endosperm. 



It is interesting to compare the young sporogonia of Mosses and 

 Liverworts with the seedlings of Phanerogams, in respect of their 

 haustorial arrangements. 128 Where the sporogonium possesses a sharply 

 differentiated basal region, the latter penetrates into the body of the 

 parent plant i.e. the gametophyte from which it derives a large 

 amount of nourishment. This haustorial foot of the sporogonium is, as 

 might be expected, provided with a specialised absorbing tissue ; among 

 Mosses the latter consists of thin-walled, more or less papillose cells, 

 while in certain Liverworts (Antkoceros, Dcndroceros, Notothylas) it is 

 represented by short tubular outgrowths, which push their way actively 

 into the tissues of the gametophyte (Fig. 98). Here again, therefore, 

 one meets with the same two stages in the specialisation of the 

 absorbing system which have already been distinguished on other 

 occasions. 



B. THE ABSORBING SYSTEM AMONG SAPROPHYTES, PARASITES AND 



CARNIVOROUS PLANTS. 



It will be found convenient to postpone the discussion of the numerous 

 intermediate stages connecting green plants with the various hetero- 

 trophic forms for the moment, and to pay attention only to the general 

 considerations that determine the structure of the absorbing system in 

 plants which are devoid of chlorophyll, and hence largely or entirely 

 dependent upon a supply of organic food-material. Evidently there are 

 two opposing [morphogenetic] influences at work in such cases. On the 

 one hand, namely, greater demands are made upon the absorbing system, 

 because in the absence of photosynthetic organs it becomes responsible 

 for the acquisition of the whole of the food-materials ; the lack of 

 actively transpiring leaves, on the other hand, permits of reduction of 

 the water-absorbing system. The other ecological peculiarities of the 

 plant will, of course, decide as to which of these factors will exert the 

 greater influence upon the structure of the absorbing system, in any 

 particular instance. 



Phanerogamic saprophytes 129 may be dealt with first. Among such 

 humus-loving plants, those which retain their green leaves and thus 

 manufacture at any rate a portion of their non-nitrogenous plastic 

 materials, have to take in considerable quantities of water, and hence 

 require a large absorbing surface. In these circumstances root-hairs 

 are needed which can not only absorb water, but also withdraw organic 

 compounds from the humus particles to which they attach themselves. 

 It is highly probable that such root-hairs (e.g. those of most terrestrial 



