79 



selves longitudinally in the equatorial plane. A separation of 

 the threads then takes place into two groups which travel to 

 either end of the nucleus. At this stage the nucleus appears to 

 consist of an oval mass of slightly staining substance, in which 

 the deeply stained threads are to be seen grouped at each end. 

 The next stage is seen in the gradual constriction or inflection 

 of the nuclear membrane, and at the same time the filaments 

 at each end of the nucleus begin to unite with each other to 

 form the daughter nuclei. A "narrow bridge connecting the two 

 nuclei remains for some time, but this is finally broken down, 

 and the two daughter nuclei are completely formed. 



Organs of Reproduction. 

 We have now to consider the way in which the Fungus 

 reproduces itself. In P. parasitica as well as in most other Fungi, 

 there are two distinct methods of reproduction. (1) Asexual or 

 vegetative, in which a certain portion of the plant is cut off and 

 from which a new plant is ultimately developed, and (2) Sexual in 

 which a new element or spore is formed by the combination (1) ^of 

 two masses of protoplasm from the same or from diflerent filaments. 



The asexual organs of reproduction are found on special 

 branches of the filament which project through the epidermis of 

 the host plant into the air, to form the white patches already 

 mentioned. These branches are known as sporophores. They 

 branch freely, and each branch becomes bifid at the tip. The 

 spores are borne on these tips. They arise as slight expansions 

 which gradually increase in size, obtain protoplasm and nuclei 

 from the filament and ai'e finally cut off by a constriction. The 

 spore when thus cut off is a somewhat oval body, full of 

 protoplasm and nuclei. These differ structurally from the nuclei 

 in the mycelium. They are round or oval bodies consisting of a 

 small central mass of chromatin surrounded by a layer of less 

 deeply staining substance, which appears to be enclosed in a 

 nuclear membrane. (Fig. V. n.) 



"When ripe the spore falls off and immediately begins to put 

 forth a tube which penetrates tlie epidermis of the host and 

 gradually develops into a new plant. 



* As will be seen later it is doubtful whether fertilisation does take place 

 in P. parasitica. 



