ALBUGO PORTULACM 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, 



