DORMANT PERIODS. 35 1 



even in a few days. At this time of the year, indeed, it does not even require 

 a favourably high temperature and an external supply of water : the shoots begin 

 to develope at much lower temperatures, and this, even when the potatoes and bulbs 

 do not receive the addition of water from without. Not only so, they will put 

 forth germinal shoots when suspended in dry air and shrivelled up by the loss of 

 water. It is evident that some internal change must have taken place in the tubers 

 and bulbs during the winter months when it is impossible to bring them into activity 

 from their state of rest, since no such change is perceptible externally, and the 

 behaviour described appears inexplicable otherwise. 



The behaviour of the Water-nut, the fruit of Trapa nutans, is perhaps still 

 more striking. If at the end of August, or in September, when they are ripe, 

 one of these is placed in a glass full of water, no germination occurs either 

 during the autumn or winter, even in a chamber where the water is constantly at 

 15-20° C; but in March or April germination begins although the water is at 

 a temperature of only 8-10° C. The most striking examples of periodic rest 

 and activity are probably afforded however by the majority of woody plants, 

 especially those which produce winter-buds clothed with scales, such as the Horse- 

 chestnut, ordinary fruit-trees, and species of Pinus and Abies. As soon as this 

 year's foliage and flower-shoots have become unfolded in the spring from the winter- 

 buds of the previous year, the winter-buds for the next year are formed in embryo ; 

 the future shoots or even flowers develope slowly within the bud envelopes, but 

 remain in an embryonic condition, and it is impossible by any means to cause these 

 embryonic shoots to develope in the autumn or the beginning of winter. On the 

 other hand, they develope in January, or better in February, if branches furnished 

 with buds are cut oiF and allowed to stand in water in an ordinary warm dwelling- 

 room — ^i. e. at a temperature of about 15-20° C. The winter-buds of trees thus 

 behave just like subterranean bulbs and tubers. 



It is by no means to be denied that in many of these cases, especially in those of 

 the winter-buds of trees, some bulbs (Hyacinthits , Crocus), etc., a considerable time 

 is necessary in order that the embryonic rudiments of the leaf-shoots and flowers 

 within their envelopes may be first so far prepared by slow growth that they are 

 suited for rapid development subsequently. The decisive point certainly does not 

 lie in this, however, as may be seen in the behaviour of the Water-nut. We find 

 the most evident and instructive cases with reference to the question here alone 

 concerned, however, in the spores of many Cryptogams. The majority of the 

 spores of Algse and Fungi, especially those produced by sexual fertilisation, 

 are distinguished as 'resting spores,' because after their formation in the spring 

 or summer they remain dormant for 8-10 months, either in water or dry, without 

 germinating, whereupon they then put forth their germinal shoots at a lower tem- 

 perature in the following spring. This peculiarity of resting spores is so much 

 the more striking since many of these plants produce simultaneously or previously other 

 forms of spores, which are capable of germination immediately after their origin. 

 As examples may be mentioned the zygospores of the Mucorini, which require 

 rest, and the conidia of the same fungus which can germinate at any time. 



It appears certain that the internal changes which take place in the resting 

 tubers, bulbs, buds, and spores, during the long pause, are promoted, in many cases 



