1896-97.] THE GAMETOPHYTE OF BOTRYCHIUM VIRGINIANUM. 273 



with a heavy oil which is not readily soluble in alcohol. They are 

 likewise occupied by a filamentous fungus which is presently to be 

 described. Figure i6 illustrates a median long-section of the prothallus. 

 At X. is seen the antheridial ridge cut lengthwise, and showing the 

 antheridia in various stages of development. The younger ones are 

 found nearer the anterior, sloping, apical region, a.p. The distribution 

 of the fungiferous tissue is represented in this figure. It is to be noted 

 that it extends forward gradually, as the prothallus increases in length, 

 by the activity of the apical meristem. The fungus never occupies all 

 the cells on the lower side of the prothallus, but leaves free always a few 

 of the lower tiers. Above, as has been alread)' stated, there is a 

 considerable mass of cellular tissue underneath the reproductive organs, 

 quite free from infection and containing a small amount of starch. The 

 symbiont is always present, as it has never been missed in the four or 

 five hundred plants which have been minutely studied. It is not possible 

 to state whether it is indifferent or beneficial to its host ; it certainly does 

 not seem to be injurious. The infected cells do not apparently suffer, 

 and perhaps the presence of oil in them, may be interpreted as an 

 indication of improved nutrition. Only experimental cultures can settle 

 this important question. 



The growing region of the prothallus is always on the upper side, 

 figure 16, a.p. It is marked by the presence of a superficial layer of high 

 columnar cells like those found at the base of the apical incision of the 

 leptosporangiate gametophyte. These are represented in figure 17. One 

 of the columnar cells, a., is in all probability, the initial cell. It is very 

 difficult to secure exactly horizontal sections of the apical region except 

 in very young plants, of which my supply was somewhat limited. These 

 were all used up for longitudinal and transverse series, and I am accord- 

 ingly unable to describe the horizontal configuration of the initial cell. 



The root-hairs are from one to four millimetres in length and are often 

 multicellular, especially when they arise from the crest or flanks of the 

 prothallium. Those which originate from the base are unicellular and 

 longer than the others. These rhizoids are generally about twenty 

 micra in width and are more or less completely cutinized. It is chiefly 

 through them that the symbiotic fungus makes its way into the prothal- 

 lium. The passage of the fungal hyphce. through the cutinized wall of the 

 root-hair, is marked by the formation of thick sheaths which surround 

 the hyphcB for ten or more micra of their course. These sheaths are 

 apparently only formed where the fungus has to penetrate an already 

 cutinized wall, and one does not find the phenomenon repeated as the 

 hyphie pass successively through the walls of the internal cells of the 



