HOOKEK. — BOTANICAL INSTRUCTIONS. 67 



obtaining many and rare species. To obtain fruiting specimens 

 choose inmost cases the least green or attractive looking specimens, 

 and even brown and dead looking patches afford the best chance 

 of obtaining fruiting specimens of the conjugatae. This follows 

 from the fact that the cells empty in conjugation, and the patches 

 hence consist for the most part of empty siliceous coats. Scyto- 

 nematous and Palmellaeeous Algae grow upon wet rocks ; the 

 former keep well enough folded in paper and left to dry, after 

 which they can be re-moistened, but the latter should be bottled." 



The Arctic Expedition affords excellent opportunities to the 

 naturalist for making observations on the power of seeds to resist 

 cold whilst retaining their vitality. To this end samples of 

 various seeds will be supplied for conducting the experiment, which 

 is of the simplest description. Certain fixed numbers of any one 

 kind of seed should be exposed to a low temperature, and sown, 

 side by side with as many that have not been so exposed, in pans 

 of earth kept moist, and the time required for the germination of 

 every seed noted. Such kinds as survive the degree of cold to 

 which they have been exposed should then be referred to succes- 

 sively longer periods of cold and to greater cold till the power of 

 germination is lost. Variations of this experiment will suggest 

 themselves to the naturalists ; equal numbers of small and light 

 seeds, and larger and heavy may be compared, which may be 

 selected by weight or by measurement. The germinated plants also 

 may be exposed to successively greater degrees of cold and the 

 results noted. Seeds may be immersed in fresh and in salt water 

 of different temperature artificially raised, with a view of testing 

 their power of resisting their influence, as may also roots of Polar 

 plants, the hybernacula or buds of such plants as Saxifraga 

 cernua. The seeds supplied are mustard, cress, radish, turnip, 

 pea, bean, sweet pea, wheat, barley, oats, maize. 



Observations are wanting of the temperature to which Arctic 

 plants are exposed during the winter when covered with snow. 

 This can be approximately ascertained by sinking a tube of wood 

 or other non-conducting material containing a thermometer 

 attached to the base of a rod of wood through the snow into the 

 soil in which the plants grow. The base of the tube should be 

 made of a conducting material which would take the tem- 

 perature of the soil, and the bulb of the thermometer should be 

 covered with wool, so that it may retain the temperature during 

 withdrawal for reading off. 



