368 G. T. HARRIS ON 



the protonema with its differentiated light-cells, for in one part a 

 thick mat of protonema and young plants may be seen while a 

 contiguous patch of adult plants bearing capsules may be practic- 

 ally without any protonema. The function of the protonema 

 being the protection and nourishment of the bud in its early 

 stages, it would obviously not be required when the plant was 

 able to maintain itself ; and as the adult plant of Schistostega 

 produces an abundance of rhizoids which fix it independently to 

 the soil, the necessity for the existence of the protonema ceases. 

 As far as the adult plant is concerned the protonema is certainly, 

 in a strict sense, not persistent, but it may always be in existence 

 in some part of the colony. It is undoubtedly a very variable 



lit''' 



Photo-synthetic s\|8tem d li^htcelb. 

 ( AJterNoll.) 



production. In some instances I have had thick felted masses of 

 bi pinnate threads, as shown in Plate 23, fig. 9, with practically 

 no light-cells ; in other growths the light-cells predominated, and 

 the simple bipinnate stage is probably the early stage of the 

 photo-synthetic system, as I have had whole masses which 

 exhibited the light-cells arranged in a beautiful bipinnate manner. 

 Noll has given a figure of the protonema which shows it as a 

 dendroid structure, the light-cells being arranged in two flat 

 tables one on either side of an upright stem, which arises from a 

 basal protonema (Fig. 2 in text). I have never seen anything so 

 regular and symmetrical as this figure of Noll's indicates. Usually 

 the photo-synthetic system, although elevated above the basal 



