xii THE BOOK OF BULBS 



It is easy to understand how great an advantage it 

 may be to a plant, in which cross-fertilisation is essential 

 to racial vigour, to open its flowers before the great 

 armies of floral rivals expose their baits to the gaze of 

 flying insects whose visits are desired. For a like 

 reason, it is advantageous to certain flowers to appear 

 late in autumn after the summer flowers have withered 

 and the competition for insect visitors has abated. These 

 also have usually woody stems, or bulbous or tuberous 

 rhizomes or roots, in which are stored reserves of starch, 

 sugar, and other foods formed in the season of sunlight. 

 Fibrous-rooted plants, on the other hand, for the most 

 part flower between the months of April and September, 

 when the daily hours of sunlight are many. 



We commonly speak of the bulbs of crocuses as of 

 tulips or of onions, but morphologically there is a dis- 

 tinction, although functionally there is little or none. If 

 we examine a tulip bulb, we find that it is mainly com- 

 posed of thick succulent scales which closely overlap 

 one another, in the centre being a flattish axis continuous 

 with the roots below, and with the leaf and flower- 

 bearing stalk above. This axis is part of the tulip's 

 stem, the fleshy scales being morphologically but modified 

 leaves whose basal portions have become swollen with 

 stores of nutriment. After the tulip has flowered, it 

 sets to work to manufacture fresh supplies of food 

 material which is sent down the stem and there accumu- 

 lated in a new bulb, formed by the development of a 

 bud contained among the scales of the old and now 

 withered bulb of the previous year. These stores 

 will, in the following season, enable the tulip to 

 cut a pretty figure before it or other plant has had time 

 or opportunity for preparing fresh supplies by the aid of 

 the spring-time sun alone. 



The so-called bulb of the crocus has a somewhat 

 different structure. The crocus " bulb" does not, like 



