334 ORGANIC GROWTH sec. 



facts brought to light by Pfeffer open a far-stretching vista 

 of possibilities witli regard to the effect of stimuli on the 

 lower oriranisms. l*fefter has shown that chemical stimuli 

 affect certain vegetable spermatozoa; that, for instance, they 

 are attracted in water by malic acid, and that they collect 

 in fine tubes filled Avith that substance, as though impelled 

 by a secret force, so that they can be captured in such tubes.^ 

 I have already referred to a similar remarkable sensibility to 

 stimuli on the part of protoplasm, at p. 312. 



It seems therefore certain that the sensitiveness of 

 protoplasm to mechanical stimuli, like that of contact, and 

 to chemical stimuli, is one of its fundamental properties. 

 Since the other stimuli, termed sense stimuli, are merely 

 more delicate kinds of one or other of these, the question 

 arises whether protoplasm is from the first sensitive to these, 

 although only in a very slight degree, or whether it has only 

 become sensitive to them by practice under the coarser 

 stimuli — has been educated to perceive them. With regard 



^ \V. Pfetfer, Lokomotorische liichtungsheivegungen durch chemische Heize, 

 Berichte der deutschen botanischen Gesellschaft, Bd. i. 1883, p. 524: "Malic 

 acid is the specific stimulus wliicli attracts the autherozooids of ferns into the 

 open archegonia. In like manner, wlien this substance is unequally distributed 

 in water the autherozooids of Selaginella move towards the spots where it is most 

 concentrated. In a similar sense cane-sugar is the specific stimulus of the authero- 

 zooids of the leaf-moss. . . . Not one particular, but every nutritious substance 

 is, when unequally distributed in solution, a stimulus to motile bacteria, which 

 move towards the richer or better nourishment. I have also found that an extract 

 of meat is able to attract the swarm - sjiores of Saprolegnia and Trepomonas 

 agilis, one of the Flagellata. All these are cases of chemical stimulation, by 

 which the motile organism is excited to travel by its ordinary means of loco- 

 motion towards the more concentrated medium, that is, in the opposite direction 

 to difl'u.sion." 



Pfeffer attracted the autherozooids of ferns witli malic acid into capillary 

 tubes, and with exceedingly small quantities of the substance : the eflfect was 

 marked even with a solution of '0001 per cent. 



We have here, then, a chemical stimulus which ensurea-fertilisation — the 

 malic acid conducts the autherozooids of ferns. Other autherozooids are influenced 

 by other such stimuli, e.g. those of mosses by cane-sugar. For further details 

 see W. Pfeffer, Lokomotorlsche liichtungsbeioegu/ngeii durch chemische Reize in 

 Untersuch. aits dem. But. Inst, zu Tubingen, Bd. i. 1881-85, p. 363. 



