172 SUMMARY OF CUREENT RESEARCHES RELATING TO 



to form a disc. This type is found in Gigartinales, Rhodymeniales^ 

 Corallinacese, most Cryptonemiefe, and certain species of GhantransiOr 

 (ISTemalionales). In the third type, the spore often elongates, then 

 divides by a cross-wall, parallel with the substratum, into two cells, one 

 of which represents the pole of the shoot, the other the pole of the root. 

 This type occurs in Ceramiaceas, Rhodomelacefe and Delesseriacese. The 

 method of culture of the germinating spores is described ; and many 

 figures are given of the various developmental stages of each of the 

 twelve species described. 



Among the many interesting points described in connexion with the 

 developing sporings is the growth of long unicellular hairs, which 

 occurred in cultures of Dwnotitia to which no additional nitrate had 

 been supplied. In all other respects the conditions of the cultures were 

 the same ; and the author concludes therefore that the hairs which 

 occur in so many algas are formed for the greater absorption of nutritive 

 substances, particularly nitrates and phosphates, from the sea-water. 



Finally, the author discusses the question of the influence of light on 

 the germination of spores, after giving the views of other authors on 

 the subject. His own experiments all point to the conclusion that it is 

 the substratum and not the direction of light that influences the 

 orientation of the germinating spore. In his own cultures the sub- 

 stratum was always horizontal, and it is therefore quite possible, though 

 not necessarily certain, that the influence of the substratum on the 

 orientation is merely the influence of gravity. This point needs further 

 investigation. E. S. G-. 



Parasitism among the Red Algae. — ^Y. A. Setchell (Proc. Anier. 

 Phil. Soc, 1918, 57, 155-72). The author begins by defining 

 " endophyte " and " epiphyte," and showing how easily both classes may 

 include species which are partially parasitic. He then summarizes 

 fully and clearly the work done on algal parasitic species, and gives a 

 list of forty-two published species, with their respective hosts. The total 

 number of genera known to the author is twenty-nine. These are all 

 reduced or condensed as to the thallus, penetrating and apparently 

 forming protoplasmic connexions with the host plants, and varying from 

 full deep red to pure shining white. Four of these genera are yet 

 unpublished, together with about nine species, of which a short resume 

 is given, all of them being in the author's possession. Of the eleven 

 families among which the parasitic genera are distributed, two — viz. 

 Gigartinacese (with five genera and twelve species), and Rhodomelaceas 

 (with nine genera and seventeen species) — contain one half or more of 

 the known genera and species. It is a remarkable fact that so many of 

 the parasitic red algage are restricted to near relatives as hosts. Theories- 

 have been advanced to account for this. The probability, as it seems 

 to the author, is, however, that the various parasites, or some of them, 

 may have originated in close connexion with their hosts by some muta- 

 tion decreasing the chlorophyll content or power in one or other of the 

 different forms of spore. Such an inducement to increase the power of 

 penetration and possible protoplasmic connexion between a spore (tetra- 

 spore or carpospore) germinating in position might, it would seem 



