642 SUMMARY OF CURRENT RESEARCHES RELATING TO 



place it close to the Mucors, and it also bears heads of conidia some- 

 thing similar to those of Rhopalomyces or (Edocephalum. The writer 

 found his species growing on decaying squashes, and subsequently he 

 cultivated it from a dying flower of Hibiscus in Florida. It does con- 

 siderable injury to squashes, spreading from the dying flower to the 

 growing fruit. The same fungus was recorded in 1875 by Berkeley and 

 Ravenel from Lower Carolina, as Rhopalomyces Cucurbitarum. It is 

 now proved to be identical with Ghoanephora americana found recently 

 by Alfred Moeller in Brazil. Thaxter does not hold that this genus 

 forms, as Cunningham supposed, a stepping-stone between the Zygomy- 

 cetes and the Oomycetes. There is no indication of heterogamy in the 

 sexual spores. Zygospores have only been seen in the species from 

 India. 



Fertilisation in Sclerospora.* — F. L. Stevens finds 40 to 50 nuclei 

 in each oogonium ; they are relatively large and fewer in comparison 

 with the size of the oogonium (45-50 //. in diameter) than usual in 

 Peronosporales. As in Albugo the nuclei in the young oogonium rapidly 

 enlarge and pass into the spirem condition ; when metaphase is reached 

 they are arranged in an approximate circle round the region that is to 

 become the oosphere, recalling the arrangement of Albugo Candida. As 

 in that species one nucleus remains behind with the coenocentrum. 

 During the completion of the mitosis the ooplasm and periplasm become 

 clearly differentiated, and there is a withdrawal of cytoplasm from the 

 periphery of the oogonium as in A. Candida and Peronospora. There is 

 throughout an unthickened region in the oogonial wall contiguous to 

 the antheridium. In history and structure the coenocentrum agrees 

 well with that of Albugo Bliti, with the exception that the central 

 globule has not been demonstrated. 



The antheridium is usually very small and is closely appressed to the 

 oogonium ; the antheridial nuclei enlarge simultaneously with those of 

 the oogonium and undergo mitosis. No receptive papilla was seen. 

 Communication occurs by the bulging and eventual rupturing of the 

 oogonial wall at this point of contact. The antheridial tube penetrates 

 the oosphere, discharging its contents before it reaches the centre. The 

 male pronucleus is slightly smaller than the female, with which it was 

 seen to fuse. 



The general bearing of the cytological evidence emphasises the 

 affinity of Sclerospora to the Peronosporaceas rather than to the 

 Albuginacess, and indicates a specialised rather than a primitive char- 

 acter. 



Oogenesis in Saprolegnia.f — B. M. Davis has studied the formation 

 of eggs and asexual spores in Saprolegnia mixta, an apogamous species. 

 The resting nucleus has a loose linin network and a nucleolus, and shows 

 essentially the structure of the nucleus of the higher plants. There is 

 one mitosis in the oogonium, the spindle being intranuclear. The 

 daughter nuclei are much smaller than their parents and some show 

 signs of degeneration, the membranes becoming indistinct and the 



* Bot. Gazette, xxxiv. (1902) pp. 420-5 (1 pi.). 

 t Op. cit., xxxv. (1903) pp. 233-49, 320-59 (2£pls.). 



