7S6 ECOLOGY 



substances such as various organic compounds (qualitative efficiency), 

 and the greater absorption of various substances, such as water (quanti- 

 tative efficiency). Perhaps another advantageous feature in hyphae is 

 the fact that cross walls are absent for long distances. Thus it seems 

 very probable that hyphae flourish much better than do root hairs, when 

 the two develop in a common medium, such as the forest humus; this 

 appears to be a consideration of great importance in connection with the 

 mycorhiza plants (p. 791). 



Saprophytism in the algae. — Algae as a class possess synthetic pigments 

 and are autophytic, these being the chief characters that distinguish 

 them from fungi; however, the saprophytic potentiality of many algal 

 forms has been established. Some plants that are classed as algae are 

 habitually saprophytic and colorless, particularly some of the Peridineae 

 and diatoms (as Nitzschia putridd) ; in Euglena and in various diatoms, 

 the members of a given species sometimes are pigmented and presum- 

 ably autophytic, and sometimes they are colorless and presumably sapro- 

 phytic. In one alga, supposed to be Carteria or a closely allied form, 

 there appears to be nutritive dimorphism, approximately half of the in- 

 dividuals in each colony being pigmented and autophytic, while half 

 are colorless and saprophytic. A cave-inhabiting form of Gloeothece 

 rupestris, namely, the variety cavernarum, habitually utilizes organic 

 food and is colorless. Comprehensive experiments show that many 

 species of the lower algae may flourish in darkness, even when organic 

 acids (as acetic acid) are the only source of carbon. If organic sub- 

 stances occur in abundance, many algae grow about as well in darkness 

 as in light; indeed, there are some forms that grow more luxuriantly as 

 saprophytes in darkness than as autophytes in the light. The abundant 

 growth of algae in water pipes and in drains doubtless is due to their 

 capacity for saprophytism. Some algae, especially those occurring in 

 lichens, almost equal the fungi in their saprophytic potentiality, being 

 able to utilize such proteins as peptones for food. 



In addition to the colorless algae noted above there are now known a 

 number of forms which lose their pigment when grown in media rich in 

 organic food (as in strong glycerine solutions), the colorless condition 

 ensuing either in darkness or in sunlight. Thus many green algae, blue- 

 green algae, and diatoms are representative mixophytes, having on the 

 one hand a capacity for independent existence, and on the other a possi- 

 bility of saprophytism comparable to that habitually exhibited by fungi. 

 Such phenomena show that the presence of chlorophyll indicates rather 



