298 BOTANY OF THE LIVING PLANT 



curvature of the fruiting stalk, as in the Earth-Nut (Arachis), or the 

 subterranean Clover. In one way or another they become covered, 

 and in the dorm:.;:t season there is plenty of time for the process. 



A latent or resting period is commonly determined by climatic 

 conditions of drought in the tropics, or of cold in temperate climates. 

 But a latent period may be imposed by the seeds themselves refusing 

 to germinate till after a period of rest. In this respect seeds vary. 

 Some will germinate immediately they are matured if the conditions 

 are favourable. It is this that makes the difficulty with cereal crops 

 in a warm, wet autumn : for those conditions stimulate immediate 

 germination, and the corn is liable to sprout in the stook before it 

 can be harvested. But as a rule a period of rest follows on ripening. 

 The seed dries out, and in that state it remains stationary, but retains 

 its vitality, being specially resistant to extremes of drought and 

 heat. An example of an obligatory resting period is seen in the 

 Sycamore. If the seeds are collected in autumn, and exposed to 

 conditions favourable for germination, they remain passive till the 

 spring, when they will all germinate almost simultaneously. The seeds 

 of the Ash and the Hornbean are said to remain dormant two years, 

 and longer periods are recorded for other plants. Others again have, 

 in addition to seeds that germinate in the first year, others which 

 require a longer rest : Laburnum, wild Mignonette, and field Clover 

 are among these, while the Cockleburr (Xanthiuip), with its two fused 

 fruits, is also said to germinate one in the first, the other in a later 

 season. 



Akin to such questions is that of the length of time during which seeds can 

 retain their vitality. This varies in the individuals of any sample of seeds 

 saved under apparently uniform circumstances. As the period is lengthened 

 the proportion of seeds that germinate diminishes. Speaking generally, oily 

 seeds retain their vitality a shorter time than starchy seeds ; and those kept 

 dry retain it longer than those kept damp. Breaking up permanent pasture, 

 or clearing old woodland gives results that indicate that seeds which had long 

 lain dormant germinate when the conditions suit them. For instance, in a 

 given case, the removal of 46 year old forest from land that had previously 

 been cultivated resulted in field-plants springing up, presumably from dormant 

 seeds. But to extend this possibility of survival to the so-called " mummy- 

 wheat " is too long a step to seem probable. A. de Candolle, after examining 

 the evidence up to 1882, concluded that no grain taken from an ancient 

 Egyptian sarcophagus and sown by horticulturalists has ever been known 

 to germinate. It is not that the thing is impossible ; but as a matter of fact 

 the attempts at raising wheat from these ancient seeds have not been successful. 

 The grain known in commerce as mummy-wheat has never had any proof of 

 antiquity of origin. 



