NATURE OF PLANTS 121 



a single plant is developed that may produce many, often thou- 

 sands of seeds, i. e., plantlets. We have already noted that these 

 may be widely distributed and so spread and multiply the number 

 of plants. Some seeds are so fine that they float away as a 

 dust, as in the orchids. Other seeds and fruits are provided 

 with hairs and wings that serve to buoy them up or promote 

 their transport by winds, as in the case of pine seeds, milk 

 weed, willow, and the fruits of maple, dandelion, etc. In other 

 cases spines and hooks or mucilage glands are developed that 

 attach them to any passing animal and so bring about a con- 

 siderable distribution. Note the common devices of this nature, 

 as in the burdock, stick tight, beggar lice, agrimony or the glands 

 on the nightshade (Circaea) and twin flower. So also seeds 

 are scattered by the spring of elastic stems and explosive fruits, 

 as in many lilies, witch hazel, violet, touch-me-not, etc. But 

 especially may seeds be looked upon as an adaptation to tide 

 the plant over seasons unfavorable for growth. In this respect 

 they may be compared to buds, which they also resemble in their 

 renewal of growth when conditions are again favorable. There 

 are some noteworthy exceptions to this statement, as in the man- 

 grove, certain oaks, and many grasses. The seeds of the former 

 plant begin their growth while still attached to the tree and a 

 similar growth has also been observed in the acorns of the 

 white oak. Grain often sprouts while in the sheaves and the 

 seeds from green tomatoes produce earlier and larger fruits. 

 However, the majority of seeds and fruits, as well as buds, can 

 not renew their growth immediately after their formation. A 

 longer or shorter resting or dormant period is required during 

 which time chemical changes occur that render the foods soluble 

 and therefore available to the young plant or embryo. For ex- 

 ample, in many seeds and buds the storage foods are in the form 

 of starch. This food is insoluble and can not be used by the 

 plant until it has been acted upon by an enzyme which changes 

 it into a soluble and readily diffusible sugar. These enzymes are 

 slowly formed during the resting period and a renewal of growth 

 is not possible until they have begun the transformation of the 

 insoluble foods into soluble forms. The changes thus effected 



