ALBUGO PORTULAC^E OR A. CANDIDA. 63 



It is possible, with patience and care, to make out the 

 parts without the use of special stains, but these afford 

 so much assistance that they should be used if possible. 1 



LABORATORY WORK. 



GROSS STRUCTURE. 



The vegetative body of the plant consists of delicate trans- 

 parent threads, ramifying through the tissues of the host on 

 which it grows, and cannot be detected without the aid of the 

 compound microscope. In a fresh or dried specimen, observe: 



1. The white blister-like pustules on the surface of the host, 

 the sori; their form. Observe the distortion and enlarge- 

 ment of the stems and leaves where the blisters (sori) are. 



2. The thin external membrane, at first entire, then becom- 

 ing ruptured in the midde. 



3. The white powdery spores, conidios pores, which drop out 

 upon jarring, if the specimen is dry. 



MINUTE STRUCTURE. 

 I. ASEXUAL REPRODUCTION. 



Mount a transverse section of a fresh or preserved specimen 

 of a stem or leaf bearing Albugo, and under low power observe: 



1. A layer of short vertical filaments, conidiophores, which 

 appear to rise from the tissues of the host and bear on 

 their free extremities: 



2. Chains of rounded spores (conidia), now mostly detached. 



3. The ruptured membrane consisting of the surface-cells 

 of the host, formerly covering the sorus. 



4. Draw. 



The vegetative portion of the plant, consisting of branching 

 filaments pervading the tissues of the host, if studied by 



1 For directions for staining Fungi see Chamberlain's "Methods in 

 Plant Histology," p. 79. 



