249 



can be In no other way tlian by Intussusception. He gives elabor- 

 ate arguments to prove that the turgor could not be sufficient to 

 account for it on the principal of stretching, says that a pressure 



■ 



of from 3,750 to 5,000 atmospheres must be assumed in order to 

 produce such a result, and that it is impossible to premise a pres- 

 sure of more than 1,000 atmospheres in a cell. Other serious ob- 

 jections are given, "and finally, because Strasburger denies that a 

 cell can grow In surface by any other process than by stretch- 

 ing, he says, admitting it to have grown by stretching, we 

 must then expect it to be proportionately thinner, but such Is 

 not the case. Measurements are given showing the wall to be of 

 uniform thickness. Therefore It is proven that these local thicken- 

 ings in the bast cells of these plants must be the result of the 



process of intussusception. 



Then he gives his reasons for concluding that in most cases of 

 thickened walls showing strlation the process of new formation 

 has taken place, a wall being built and then added to the previous 

 one. He says, admitting this latter statement proven, " Still the 

 real question is not touched, for who can say how this new wall 

 increased In thickness in its process of growth, whether by appo- 

 sition or intussusception." In the case of the growth of the 

 widened places in the bast fibers, however, a definite point Is 

 gained ; If the proofs are satisfactory then we may hold that the 

 theory of growth in thickness by intussusception In some cases Is 



established. 



While the writer was studying the development of wings on 



the stems of the genus Euonymus one or two instances of peculiar 

 growth were noticed. About eighteen different species or varie- 

 ties of this genus were studied, but only one of them showed this 



nistifi 



peculiarity in wall formation. This was Euonymus an 

 var. purpurea; the specimens were obtained from the nursery of 

 Thomas Meehan, near Philadelphia. This species has the usual 

 four-angled stem with slight but perfectly developed wings along 

 these angles. It will be necessary here to repeat a little from the 

 work on cork wings referred to above : " A cross-section at the 

 distance of ^ centimeter from the growing tip of stem shows the 

 tissues of the rind In a formative stage. The outer wall of the 

 epidermal cells is covered by a thin cuticle, the cells themselves 



A 



