STRUCTURE AND DEVELOPMENTAL RATE 229 



plant conditions with animal development I very fully recognize. 

 There is, however, evidence of certain actual similarities which, 

 along with deductions from my experiments on embryos, may 

 serve to elucidate the problem of organ formation to a consider- 

 able extent. Particularly suggestive is an examination of — 



a. The growth influence of the apical or primary hud over the 

 secondary and potential buds in plants 



It is commonly observed that when a number of beans or other 

 seeds are planted in a row under similar* conditions of soil and 

 moisture, the initial bud from each seed sprouts upward and 

 grows to a definite extent and then temporarily stops. On exam- 

 ining the row of young shoots, each with two horizontally spread 

 terminal leaves, it is generally found that all are very nearly of 

 the same height. Should a certain part of the row occur in a 

 more favorable environment than another the sprouts in this 

 part may grow higher than in the others, or should certain seeds 

 have been defective or their environment in the row unfavor- 

 able, the sprouts in such cases are lower and smaller than the 

 average. These low small plants seem as a general rule unable 

 to overcome their inferior condition during later growth and either 

 die or form very poor specimens. The small sprouts would appear 

 to have suffered an arrest during their early development in 

 consequence of which they generally fail to be normally large 

 fruiting plants. 



The original shoot is entirely formed from the food contained 

 within the cotyledons and the water of absorption. After attain- 

 ing a definite length, it stops or slows its progress until the roots 

 become sufficiently established to obtain further food and mois- 

 ture from the soil. On becoming properly rooted the apical 

 bud then grows upward from a point between the two original 

 leaves and from this the development of the plant proceeds. 

 We thus have an interruption, after the formation of the original 

 sprout, similar to that found in the development of many verte- 

 brates and from a somewhat similar cause. Here the plant could 

 not continue to grow until certain substances were supplied by 



