100 PLANT-LIFE 



owing to their parasitism have no chlorophyll; such 

 are undoubted descendants from green ancestors, and 

 they serve to illustrate the fact that complete parasitism 

 involves loss of chlorophyll, and the consequent atrophy 

 of all power of elaborating carbon compounds from 

 inorganic materials. However, few Fungi betray any 

 close resemblance to their green ancestors; they are 

 far-removed relations, and have become so modified 

 in structure and development, in adaptation to habit 

 and environment, that their pedigree cannot be traced. 

 But there are some Fungi with most evident Algal 

 affinities, and it will be interesting for us to consider 

 the life-cycle of one of them. 



Fungi of the genus Pythium, belonging to the group 

 OOMYCETES (Gr. don, an egg; mycetes, fungi) are respon- 

 sible for much damage to seedlings, on which they are 

 parasitic. They cause the disease known to gardeners 

 as "damping-off "; it occurs very commonly in propa- 

 gating pits that are allowed to become too damp and 

 warm, and to which light and air are not allowed 

 sufficient access. A plentiful supply of Pythium Barya- 

 num may be obtained thus: sow seeds of the common 

 garden Cress (Lepidium sativum) in a flower-pot, satu- 

 rate the soil with water, cover the pot with a piece of 

 glass to exclude overmuch air and ensure a moist 

 atmosphere, and as the seeds germinate, and the seed- 

 lings grow, see to it that the water-supply is super- 

 abundant. Some of the seedlings will soon display 

 weakness; their stems will bend over, and it may be 

 observed that they show the greatest weakness at the 

 point of curvature; ultimately the diseased stems will 

 fall, lose colour, and become rotten. Pythium Baryanum 



