220 STEUCTUEAL BOTANY 



intercellular spaces, but can enter the cells themselves. 

 Thus the whole plant comes to be infected, and is 

 traversed throughout by the branched mycelium of the 

 parasite, which lives at its expense. 



In the First Part of this book (p. 216) we learnt 

 that there are chemical bodies in plants called ferments 

 (or enzymes), which have the power of changing the con- 

 stitution of other organic substances, converting solids into 

 liquids, and indigestible substances into such as are avail- 

 able for nutrition. The example we specially mentioned 

 was diastase, which converts starch into grape-sugar, 

 but numerous other ferments also occur in plants. Now 

 parasitic Fungi have the power of secreting ferments, 

 which play a very important part in bringing their victims 

 into subjection. The advancing tip of a mycelial hypha 

 secretes a ferment which dissolves the cell-wall lying 

 in its way, and so enables the Fungus to enter living 

 cells, while other bodies of the same class bring the 

 proteids and other organic substances of the host into 

 a condition in which the parasite can assimilate 

 them. 



In this way, then, the Pythium makes itself thoroughly 

 at home in the body of its victim, infests it in every 

 part, and eventually completely destroys its tissues, 

 converting their materials to its own use. Often the 

 hyphae leave the host, and grow out upon the soil until 

 they reach other victims, which they then infect. In 

 the mean time the Fungus does not neglect to make 

 provision for future generations. The reproduction 

 takes place in two ways, asexual and sexual. We will 

 first describe the former. 



