PARASITIC AND SAPROPHYTIC PLANTS. 



45 



after invasion by the fungus, provided there be suitable conditions of 

 culture as well." These consisted of a certain degree of moisture for 

 Cypripedium, but not for Cattleya, as this latter is naturally a xerophytic 

 epiphyte ; thus M. Bernard expresses it : " Cattleya accepted readily an 

 aerial life, while Cypripedium prospered only upon a medium constantly 

 moist." Hence, he adds, " Cattleya must have two conditions for successful 

 germination, epiphytism and being infested by the fungus." 



Otherwise " the ' spherules,' i.e. embryos, die without having passed a 

 diameter of 500/x to 600u, and without forming a leaf." " In the absence 

 of the endophyte the differentiation of hairs is possible, but their growth 

 never takes place." 



Bletia* exhibits a peculiarity distinguishing it from Cattleya and 

 Cypripedium in germination. The embryo is a little more differentiated, 

 having a rudimentary cotyledon in the form of a semicircular elevation. 

 It can grow to a certain extent without the endophyte, but not longer 

 than three months, when it dies from below upwards. This is the critical 

 period, when it requires the endophyte. This first penetrates the basal 

 cells of hairs of the hypocotyl, but subsequently the hairs themselves. 

 The internodes successively infested accelerate their development, as soon 

 as they are invaded, by individual growth of the cells. The endophyte 

 thus " acts at a distance," as it enters them only after the internodes and 

 hairs have completed their growth. 



The plantlets produce no roots if uninfected, but after infection they 

 are capable of making them through the indirect stimulation of the 

 fungus. 



In practical cultivation, to obtain success, orchids must be sow^n in an 

 infected soil, in which the same species has grown ; but other conditions 

 are necessary, as a proper degree of moisture, of temperature, of light and 

 aeration. 



Although the undifferentiated seeds of orchids appear incapable of 

 germinating without the "start " given to them by the stimulus of the 

 endophyte a large number of plants are now known to be infested by 

 endophytic fungi, which are more strictly to be called parasites. M. Gal- 

 laud describes and figures roots invaded by endophytes in species of 

 Banunculus, Parnassia, Tamus, Arum, Allium, Buscus, Paris, Ornitho- 

 galum, Colcliicum, Sequoia, Angiopteris, Ophioglossum, and Pellia. 



After penetrating the epidermis the mycelium either passes along the 

 intercellular passages or becomes intracellular, when it coils up, making 

 "tangles" (pelotons) and throwing out "tufts" (arbuscules) of finely 

 dichotomising branchlets. These absorb the starch in the cells, converting 

 it into sugar. The nucleus and protoplasm do not appear to be affected, 

 at all events materially, for they secrete a ferment which, in turn, destroys 

 the fungus, which is consumed by the host. As the endophyte only 

 attacks the starch and the pectic " middle layer" of the cell-wall, M. Gal- 

 laud calls the mycorrhiza an "internal saprophyte," which ends by being 

 consumed itself. 



Such is the brief description of some of the peculiarities of these 

 remarkable plants. They point out the wonderful property of self- 

 adaptation which runs through the whole of the vegetative world, fitting 

 * " Recherches Experimentales sur les Orchidees," Rev. Gen. cle Bot. xvi. p. 405. 



