732 EXPERIMENT STATION RECORD. 



Cuscuta it is attempted to deteruiiue wlaetlier sieve plates are ever formed in 

 compound vralls separating the cells of the host from those of the parasite. 

 After a brief discussion of the histology of Salvia and of Cuscuta, the author 

 gives the results of her investigations on the relations that exist between host 

 and parasite. The hosts examined were Salvia sp. (perennial) and Vitis sp., 

 and the parasite C. reflexa. 



It was found that the development of the sieve plates and sieve fields in the 

 phloem of Salvia and Cuscuta agreed in all essentials with those of Vitis and 

 Laminaria. The invading haustoi'ium of Cuscuta was found to consist of a 

 brush-like group of hyphse, the central ones of which push into the pith or fuse 

 with the xylem of the host ; the ones next surrounding these fuse with the 

 sieve tubes, while the peripheral hyphfe of the brush remain in the cortex. 

 The main mass of the originally separate hyphine form in the mature haustorium, 

 by lateral fusion with one another, a compact tissue. Each hypha composing 

 the tissue becomes subdivided into a number of cells forming a strand, ^^'hen 

 the tip of the hypha is connected with a sieve tube of the host, tliis strand of 

 cells develops into a strand of short sieve tubes. Connecting threads and sieve 

 tubes are numerous in the subdivision walls, but are never foiuid in the fusion 

 walls between the originally separated hyphse. 



Preparatory to the formation of a junction with a host sieve tube an invading 

 hypha lays itself alongside the sieve-tube wall, so that the two come into lateral 

 contact. The mucilaginous wall of the parasite where it touches a sieve area 

 is then absorbed, and the naked j^rotoplasm of the hypha applies itself to the 

 sieve area of the host. The junction sieve plates and sieve fields in all cases 

 exactly resemble those of the host under normal conditions. The translocation 

 of food substances from host to parasite appears to be in the nature of a 

 passive filtration. This arrangement p)-obably disturbs as little as possible the 

 normal mechanics of the sieve tubes of the host, and insures for the parasite 

 a long-continued supply of food. 



The influence of low temperatures on the distribution of the giant cactus, 

 F. SiiREVE {Plant World, 1/, (1911), No. 6, iw. 136-L',6, figs. 3).— From a study 

 of the effect of freezing on the giant cactus the author comes to the conclusion 

 that the occurrence of a single day without midday thawing, coupled with a 

 cloudiness that would prevent the internal temperature of the cactus from 

 going above that of the air, would result in the destruction of this species. A 

 study of the climatological records and the known facts of its distribution seem 

 to confirm this explanation of the limitation of its northeni distribution. 



Climatic selection in a hybrid prog'eny, D. T. MacDougal (Plant World, IJf 

 (1911), No. 6, pp. J 29-131, fig. 1).- — A report is given on observations made on a 

 number of acorns of Quercus heterophylla, a species believed to be a hybrid 

 between the willow oak (Q. phellos) and the red oak (Q. rubra). 



A number of these seedlings, which were obtained on Long Island, were 

 transferred to the Desert Laboratory at Tucson, Ariz. The entire lot cast 

 their leaves and were dormant on December 10, 1907. In 1909 the only plants 

 which had survived were 5 of the nan-ower-leaved types, and in 1910 all had 

 perished. 



The observations seem to indicate thnt the qualities of the i*ed oak were least 

 favorable to endure the desiccating action of the desert climate. It was en- 

 dured longer by the narrower and more indurated leaves resembling those of 

 the willow oak. 



