380 University of California Publications in Botany [Vol.6 



growing in the same habitat. I suspected the color to be due to the 

 death of the plants on account of their exposed condition, but a 

 casual glance with a hand lens revealed the presence of myriads of 

 small spherical cells of an endophytic unicellular green alga. Material 

 was taken to the laboratory, sectioned and studied. It was found 

 that mj^riads of these plants in all stages of development were inhab- 

 iting the thick gelatinous walls of the Porphyra cells. I began at 

 once to search through tlife literature to determine first to what genus 

 it seemed most closely allied, and second to determine whether it had 

 previously been characterized specifically. The first task has proven 

 to be by no means a simple one. The second one was fairly readily 

 decided. Nothing, so far as I have been able to determine, has yet 

 been discovered that is just like it. It seems certainly to belong to 

 the Protococcaceae, and seems most closely related to the two genera 

 Chlorochytrinm Cohn and Chlorocystis Reinhardt. The limits of 

 these two genera are not well defined, which makes it more or less 

 presumptuous on the part of any one who attempts to ally, with 

 much degree of certainty, a new species with either. Recently West 

 (1916, p. 212) has gone so far as to reduce Chlorocystis, along with 

 three other genera of Wille's group Endosphaereae to synonomy, 

 retaining Chlorochytrium, it being the oldest, as sufficient to include 

 the other three, Avhich were founded upon characters which in his 

 judgment are of minor importance, not cardinal enought to be ranked 

 as generic. A brief resume of some of the more important writings 

 concerning these two genera may be of some value at this juncture. 

 It is not intended to be complete by any means. Many other valuable 

 papers bearing on the subject have been consulted. The chief points 

 at variance between the two genera are, the method of formation of 

 "gametes" and "zoospores," the matter of their conjugation, the 

 number of their cilia, the shape of the chromatophores and the num- 

 ber of pyrenoids. 



Chlorochytrium is the older of the two genera, and was established 

 by Cohn in 1872 (1872, p. 87), based upon a form endophytic in the 

 fronds of Lemna trisulca, which he named C. Leninae. He says of 

 the zoospore formation: "plasmate viride primum in segmenta 

 majora diviso, dcin secedente in zoosporas innumeras pyriformes 

 virides processibus tubulosis extus emissas. " This method of zoo- 

 spore formation does not conform to that occurring in the plant under 

 consideration in Porphyra. Wright (1879, p. 355) published a new 

 species of Chlorochytrium which he dedicated to Professor Cohn. 



