92 



GENERAL BIOLOGY 



We will first consider a large and important ecological 

 group of organisms that we recognize as plants although they 

 do not contain chlorophyl, and they do require much the 

 same food as animals; after that, two other groups with 

 characters so intermediate that they are discussed in text 

 books of both botany and zoology at the present day. 



I. PLANTS THAT LACK CHLOROPHYL. 



The most important common characteristic of the large 

 ecological group of organisms we now come to consider, is 

 physiological: lacking chlorophyl, they have abandoned 

 the primary plant function of gathering food m.aterials 

 directly from the inorganic world. They must have organic 

 food. They can derive no energy from the sun, and they 

 thrive often quite as well without sunlight. They use the 

 same foodstuffs as animals: yet in structure and growth - 

 habit they are plants very much like green species of 

 parallel development. 



Yeasts. — These are unicellular chlorophyless plant's of 

 the group of fungi. Isolated cells have, save for their gray 

 color, much the appearance of single cells of protococcoid 

 algae. They have cellulose in their walls ; their T)rotoplasm 

 is somewhat more granular, contains minute fat droplets 

 and is without a trace of chlorophyl. 



The process of cell multiplication is peculiar. It is called 



budding (or gemmation). Mi- 

 nute processes are pushed out 

 from the side of the cell, and these 

 grow up gradually to full stature, 

 adhering for a time to the parent 

 cell. Often the new cell starts 

 buds of its own before it is fully 

 grown itself. Thus while grow- 



development; c, spores, formed • „ „,,-^-f-1^7- +Vip ppllt: pnmp fn "hp 

 on drying, four within each cell mg qUlCtly one CCliS COmC XO DC 



^^"- assembled in little clusters or 



families of cells (torulcu), as shown in fig. 55. 



Fig. 55. Yeast, a, a single cell 

 showing nucleus (dark colored), 

 two vacuoles, and numerous 

 fat droplets ; b, clusters of grow- 

 and budding yeast cells 

 (torulae), in various stages of 



