Reproductive Organs. n 



example and it applies to other genera as well the complete cycle is 

 designated Eu-puccinia, and represented diagramatically as O., I. II 

 III., IV. 



Then the stage in which the uredo does not appear is known as 

 Pucciniopsis, and represented by O., I., III., IV. Again, the germinat- 

 ing sporidiolum may produce a mycelium which bears spermogonia and ure- 

 dospores, thus skipping the aecidial stage. This stage is called Brachy- 

 puccinia, and represented by, O., II., III., IV., or the spermogonia may like- 

 wise be suppressed when practically only half of the cycle is retained, and 

 it is known as Hemi-puccinia, represented by II., III., IV. This is a stage 

 which is probably based upon imperfect observation, and the presumed 

 absence of the spermogonia. Further, the germinating sporidiolum may skip 

 the aecidial and uredo-stage and produce the teleutospore direct, with its 

 accompanying spermogonium. This is known as Lepto-puccinia when the 

 teleutospore germinates immediately, and Micro-puccinia when it undergoes 

 a period of rest. lit' would be represented diagramatically as O. III., IV. 



As might be anticipated, the greatest number of species have a complete 

 life cycle, and next to that come probably- those species in which the life 

 cycle is reduced to its lowest limits, thus showing that the aecidial and 

 uredo generations may be dispensed with. In the former case (there is, as 

 it were, a succession of forms adapted to the varying seasons, well fitted to 

 meet any sudden changes, and living upon the same, or having a change of 

 host-plant as may be found most convenient, while in the latter the change 

 consists not in the variety of spore-forms, but in having a general purpose 

 spore, which can either germinate upon the living plant as soon as it reaches 

 maturity or undergo a period of rest in ithe decayed organic matter before 

 producing sporidiola. Hollyrock rust, or Puccima malv ace arum, is a good 

 illustration of a single-spored form adapting itself to the most varied con- 

 ditions, and making its way in the world. 



The complete scheme for grouping Puccinias, according to the alterna- 

 tion of their spore-forms, is as follows: 



Eu-puccinia, O., I., II., III., IV. 

 Pucciniopsis, O., I., III., IV. 

 Brachy-puccinia, O., II., III., IV. 

 Hemi-puccinia, II., III., IV. 



Lepto-puccinia, O., III., IV. (Teleutospores germinating imme- 

 diately). 



Micro-puccinia, O., III., IV. (Teleutospores germinating after 

 a period of rest). 



REPETITION OF SPORE-FORMS. 



In connexion with the suppression or omission of spore- forms, we may 

 also consider the repetition of spore-forms, because it would appear that 

 in many instances the suppression is brought about or initiated by one of 

 the spore-forms being able to repeat itself in the course of the cycle, and 

 thus making up for the loss of one member of it. It is the doctrine of 

 substitution in another form. This will be more conveniently dealt with 

 when treating specially of the aecidio and uredo spores, where it will be 

 seen that when the uredo generation is suppressed or omitted, the aecidio- 

 spores often repeat themselves, and when the aecidial generation is 

 omitted the uredospores repeat themselves. 



INVESTIGATION OF SPORES. . 



Th.? microscopic investigation of rust spores is comparatively easy, 

 although k requires careful observation with regard to their minute details. 



