PTERIDOPHYTA. 137 



The entrance of the living spermatozoid into the neck of the arche- 

 gonium and its passage down to the egg is easily followed. In fact, 

 the phenomenon is a matter of common observation in elementary 

 classes. It is only necessary to mount prothallia with mature arche- 

 gonia ventral side up in a drop of water, to which are added several 

 clean male prothallia that contain ripe antheridia, and which have been 

 kept in dry air for a short time previous to the operation. The ripe 

 archegonia will open, and in a few minutes numerous spermatozoids 

 which have escaped on being placed in the water will be found swim- 

 ming about the opening of the archegonium, having been attracted 

 thither by the extruded substance. Many enter the neck, and several 

 may reach the egg-cell. The author has observed instances in which 

 the number of spermatozoids endeavoring to enter the archegonium 

 was so great that they formed a plug which almost completely closed 

 the opening in the neck. 



Since the interesting researches of Pfeffer ('84) it has been known 

 that the mucilaginous substance formed from the neck-canal and 

 ventral-canal cells acts as a chemotactic stimulus upon the spermato- 

 zoids. Pfeffer found that the spermatozoids of ferns are attracted by 

 malic acid and its salts in very dilute solutions. A solution of o.ooi grm. 

 per cent, is sufficient to bring about a positive chemotactic reaction. 



Buller (1900) found that in addition to malic acid and its salts, many 

 organic and inorganic salts, widely occurring in the cells of plants, 

 exercise a positive chemotactic stimulus upon the spermatozoids of 

 certain ferns. Among the organic salts which were found to attract 

 are tartrates, potassium oxalate, potassium acetate and sodium formate. 

 Among the inorganic salts are phosphates, sulphates, potassium nitrate 

 and potassium chloride. Organic substances which were found to act 

 indifferently are grape sugar, cane sugar, lactose, amylodextrine, 

 glycerine, alcohol, asparagin and urea. "Inorganic salts not appre- 

 ciably attracting are the chlorides and nitrates of sodium, ammonium 

 and calcium, and also lithium nitrate. Of the four free acids which 

 seem to be most widely found in cell-sap, namely, malic, oxalic, tartaric 

 and citric, only malic acid attracts." The concentration of malic acid 

 which gives the most pronounced reaction is o.oi grm. per cent., 

 while that which gave just an appreciable reaction was o.ooi grm. per 

 cent. With potassium nitrate no attraction could be detected at 0.05 

 grm. per cent., whereas there was a slight one at o.i per cent. 

 Roughly estimated, therefore, malic acid attracts fifty times more 

 strongly than potassium nitrate. Strong solutions repel. 



Attempts have been made to elucidate the phenomena of chemotaxis 



