REPORT OP COMMITTEE ON PUBLICATION 133 



conidium and the sterigma that it bulges out on either side. Mangin (1891) 

 on the other hand, having made a complete study of this subject, figures 

 this disjunctive wall as lenticular. He claims that it is composed of callose 

 which is, however, insoluble in water but explains this anomaly by the 

 theory that there is some chemical change in the composition which renders 

 it soluble. 



In size the conidia average from 11 to 18/i by 15 to 31/t but in certain 

 cases are much larger than this. Istvanffi (1913) distinguishes three types, 

 the microconidia, which are of the size and shape usually observed, the 

 macroconidia, having a size of 25 to 35/u by 40 to 55/i and finally the megalo- 

 conidia which are much larger than the macroconidia, more or less globose, 

 contain 15 to 20 nuclei and which are produced without the intervention of 

 a sterigma. 



At the small end of the conidium there are usually two minute projec- 

 tions, the remnants of the attachment to the sterigma. At the opposite, 

 larger end is a papilla or projection through which germination occurs. 



The thickness of the wall of the conidium lies between that of the 

 conidiophore wall and the mycelium. It is practically uniform except at 

 the papilla where it is very thin and delicate. The composition is the same 

 as that of the conidiophore, staining reddish-purple with zinc chloriodide 

 except at the papilla which remains colorless. Within each conidium there 

 are several nuclei corresponding to the zoospores which are ultimately 

 formed in it. 



On susceptible varieties, like the Delaware, Niagara and V. bicolor, the 

 downy mass of conidiophores and conidia is usually very dense and when 

 disturbed, a tiny white cloud of spores arises. On the more resistant 

 forms the growth is only slightly developed even under the most favorable 

 conditions, appearing most frequently in isolated clusters which correspond 

 to the brown punctations on the upper surface. 



The Sexual spores, oospores, are formed in the intercellular spaces 

 largely within the palisade or spongy parenchyme tissues of the leaf, and 

 almost invariably closely adjacent to the principal veins. The writer has 

 very seldom found them in the tissue about the margin or in the blade of 

 the leaf. Bailion (1888), Istvanffi (1913) and Lamson-Scribner (1886) have 

 reported finding them in the cortex of the stem and in the berries. 



The development of the oospores has not been clearly followed but 

 several different stages have been observed and in order that these may be 

 correctly interpreted and arranged in their proper sequence, a comparison 

 is made here with the oospore development of Plasmopora alpinum, described 

 by Rosenberg (1903). 



The oogonium is multinucleate (PI. IV, fig. 1) and number of nuclei 

 counted in one case being about forty. This is very similar to the oogonium 

 of P. alpinum which Rosenberg states has forty-five. In the case of P. 

 alpinum the antheridia are ciavate and contain about four or five nuclei. 

 Though many hundreds of stained sections have been examined, the writer 

 has only once observed a structure which might be interpreted as an 

 antheridium. It was much smaller than the oogonium, ciavate and arose 

 from the hyphae immediately beneath the former (PI. IV, fig. 2). Both 

 Viala (1893) and Cornu (1882) figure similar structures but Farlow (1876) 



